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Saturday, July 04, 2009 |
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Home . News . Education . Health . Shopping . Religion . Immigration . Jobs . Teachers . Web Directory . Awami Masail |
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Saturday, July 04, 2009 |
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Home . News . Education . Health . Shopping . Religion . Immigration . Jobs . Teachers . Web Directory . Awami Masail |
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Diversity
in Life Form
Chapter 4
= Kingdom Monera =
· Kingdom Monera is the first kingdom of living beings according to the latest classification of Robert Whittaker.
· In this kingdom, are included all non cellular or acellular living beings having incapient nucleus i.e. Genetic mass or DNA is not confined in a nuclear membrane bounded nucleus.
· Such living beings are called Prokaryotes e.g virus, bacteria and blue algae.
Virus
Introduction
It is non cellular smallest organism and probably the most primitive creature on earth. The word virus is a Latin word which means Poison. A Russian scientist “Ivanowsky” discovered it as a living organism and a particle in 1892 A.D. An American biologist “Stanley” isolated “Tobacco Mosaic Virus” from infected leaves in the year 1935 A.D.
Habits
Virus has dual characters i.e. within host cell it is living, active and replicating but outside the host. It is a dead crystal, completely inactive and may remain so for centuries. Virus never grows and reproduces outside the host cells. Therefore it is an “Obligatory Prasite”.
Types
Virus is a very tiny creature whose structure activities and types can only be studied by means of an “Electron Microscope” with a magnification power more than 0.1 million nanometer. Virus measures about 17-450 milli microns.
According to the type of host, virus are of three types namely:
1. Animal virus
2. Plant virus
3. Bacteriophage
Structure
Viruses are of different shapes i.e. spherical, Tetrahedral, Polygonal, Rod shape, polyhedral or Tadpole shaped. Here, structure of a bacteriophage tadpole virus is given as an example.
Example - Bacteriophage
Virus is neither animal nor plant therefore it is deovoid of cell membrane or cell wall. Externally it is covered with a rigid protein coat called “Capsid”. It is broader at one end and narrower at the other. Broader end is called “Head” and narrower end is called “Tail”. The inner cavity contains DNA. The tail is also hollow internally, this cavity is called “Core”. Tail also has got protein fibrils for movement and Antigenic proteins for attachement with the host.
Life Cycle of Bacteriophage
Bacteriophage means “bacteria eater”. The name is given due to the fact that these viruses infect bacteria and live as their parasite.
Lytic Cycle
Phage virus attaches itself with the bacterial cell wall by means of “tail piece” and secretes enzyme called Lysosome, it dissolves the bacterial wall through which DNA takes control of Bacterial DNA and its Biochemical acitivities. In this “Master slave” relationship, viral DNA initiates Bacterial enzyme system to produce nucleic acids and proteins required for viral “Replication.” Therefore a large number of viruses are produced on expense of Bacteria, as a result Bacteria is “Internally eaten” and finally disintegrades, Newly formed viruses set free and attack other bacteria for a new cycle. Such a cycle is called Lytic cycle.
Lysogenic Cycle
In some instances, viral DNA combines with the bacterial DNA in such a way that instead of “Master slave relationship” a “great host” relationship takes place in which bacterial DNA is not harmed. When bacterial DNA repticales, viral DNA also replicates simultaneously. So a number of generation can be produced unharmed. This mutual cycle is called Lysogenic cycle.
Sometimes the “guest” viral DNA reactivates to star Lytic Cycle.
Bacteria
Introduction
Bacteria or Schizomycophytes were first discovered by Antoni Van Leeuwenhock as the smallest and simplest known living creatures.
Occurrence
Bacteria are omnipresent i.e. they are present every where except five. They are able to survive in extremes of environmental conditions i.e. below 0°C and upto 150°C.
Shape and Size
Bacteria are very small, nearly 0.2 to 2 in width and 2 to 10 in length. Bacteria are classified according to their shape as follows;
1. Cocci
These are spherical bacteria and they are non flagellate. If formed solitary (singly) each one is called “Micro coccus”. If they are paired then they are called “Strepto cocci” and if they form bunches or clusters they are called “Styphlococci.”
2. Bacilli
Oval or Rod shaped Bacteria are called “bacilli”. They may be micro, diplo, strepto or staphylo bacilli.
3. Vibro or Coma Shape
These bacteria resemble english coma(,) in their shape. They are always found singly.
4. Spirilla
These bacteria are spring or “Cork screw” shaped and are always solitary.
Structure
Structurally, bacteria are almost similar. A typical bacillus is given as an example.
Cell Wall
Each bacterium posses a cell wall as an outer covering. It is made up of a complex of sugar with amino acids or sometimes contains “Chitin”. Cell wall is thick and rigid. In unfavourable conditions, some of the bacteria enclose themselves in a polysaccharide capsule.
Cell Membrane
It is also called “Plasma Membrane,” it surrounds the cytoplasm. It is made up of lipo-protein; a complex of lipid and proteins. Cell membrane is “Osmo-regulatory” and porous. It also performs respiration.
Cytoplasm
It is the fluid ground substance, which fill the inner space of cell. Cytoplasm appears granular containing “Ribosomes”. However endoplasmic reticulum, mitochondria and Colgi body are absent. Few small vacuoles are found scattered in the cytoplasm. They contain Glycogen particles as reserved food.
Incepient Nucleus
Being Prokaryote, Bacteria are devoid of membrane bounded complete nucleus. They lack nucleolus and Nuclear membrane. Genetic material or DNA is found in the centre of cell as cencentrated mass or strands called “Chromatin bodies.” Such type of incomplete nucleus is called “Incapient Nucleus.”
Flagella
Some of the bacteria are provided with cytoplasmic fibrous structures called “flagella,” they are meant for locomotion.
FIGURE
Nutrition
According to the mode of nutrition, bacteria are of two type:
1. Autotrophic Bacteria
2. Heterotrophic Bacteria
1. Autotrophic Bacteria
Bacteria capable to produce their own food material are regarded as Autotrophic Bacteria. They are of two types:
(a) Photosynthetic Bacteria
these bacteria contain Bacterio chlorophyll and chlorobium-chlorophyll and with the help of these pigments produce glucose and Glycogen by means of photosynthesis.
(b) Chemosynthetic Bacteria
These bacteria contain different type of enzymes, which oxidize certain food components or compounds anaorobically to obtain energy. The degraded products are recycled and resynthesized into food.
2. Heterotrophic Bacteria
Heterotrophic bacteria are of following three types:
(a) Saprophytic Bacteria
These bacteria obtain food from dead organic material by decomposing their complex compounds like proteins, fats and carbohydrates into simpler compounds like H2O, CO2, NH3 and Nitrates.
(b) Parasitic Bacteria
These bacteria live on living hosts i.e. animals or plants and obtain their nutrition from them and ultimately harm them by producing serious diseases. Parasitic bacteria may be obligate or facultative parasites.
(c) Symbiotic Bacteria
These are the Bacteria and live in association with another living being taking benefit from him and providing the same in return. Examples are Rhizobium Radiciols which live in nodules over roots of Leguminous plants taking shelter and food from these plants and produce and provide fertilizer in the form of Nitrates.
Reproduction
Bacteria reproduce by two methods:
1. A sexual Reproduction
2. Sexual Reproduction
1. A Sexual Reproduction
It is of two main types which are explained below:
(a) Fission
It is the usual method of reproduction. Bacteria first replicate their DNA and then the cytoplasm splits into two halves by means of a middle constriction. It is the simplest and less time consuming method.
(b) Endospore Formation
It is the method of survival in unforable circumstances rather than reproduction. In this method, cytoplasm along with DNA shrinks and accumulates at one side within the cell of Rod Shape bacteria. Later on a hard impervious “Cyst” is formed around cytoplasmic mass, the rounded confined encysted mass is called “Endospore.” On return of favourable condition cyst breaks and cytoplasm activates and enlarges to form new bacteria. Endospore can survive for months without any harm to bacteria.
2. Sexual Reproduction
It is not true sexual reproduction but exchange of DNA or genetic recombination between bacteria. It can take place by means of following methods:
(a) Conjugation
Definition
“Transfer of DNA from one to another bacteria through a tube (conjugation tube) is called Conjugation.”
Explanation
Joshua and Fatum in 1946 selected a “wild type” of E. Coli bacteria for their experiment. These bacteria were capable to sybthesize different Amino acids (say A, B, C, D, E and F)
These wild type bacteria were irradiated by X-Rays by which two new strains are obtained. These strains are:
(i)
Mutant X (capable to
synthesize A, B and C amino acids)
(ii)
Mutant Y (capable to
synthesize D, E and F amino acids only)
In the next step these bacteria were cultured together in a nutrient medium. By careful analysis it was found that a new strain came into existence which is unable to synthesize any of the amino acids A, B, C, D, E or F. Similarly parent wild type bacteria were also obtained. The only logical explanation about this happening is that the Bacteria conjugated i.e. exchange their DNA through a conjugation tube.
(b) Transduction
Definition
“Transduction is the process of recombination in which genetic material or DNA of one bacterium is transferred to another bacterium through a third party, the transfering third party is a bacteriophage virous.
Explanation
This type of DNA recombination was discovered by Joshua Lederberg and Zinder in 1952. When a bacteriophage virus attacks a bacterium (donor) and combines its injected DNA with bacterial DNA, during DNA replication, viral DNA receives some of the bacterial DNA i.e. of donor. When viruses are released or set free from destroyed bacteria, they have got not only viral DNA but some amount of Donor (Bacterial) DNA too.
When these “mixed DNA” phage viruses attack some new bacteria (recipient) and start “Lysogenic cycle”, the recipient not only replicates its own DNA but also the DNA of phage and donor’s DNA. The progency not only shows characters of its own but also the character of donor. Thus phage virus is the 3rd party in this recombination.
Transformation
A British Nobel prize winner bacteriologist “Fred Griffith” discovered the phenomena of transformation of Genetic charters in bacteria. According to him:
“Bacteria can transform (i.e. undergo genetic change) by receiving genetic information from some other bacteria and acquire his characters.”
Griffth discovered this phenomena accidentally during his work on two shains of Pneumo Cocci one of the specie was smooth, capsulated example virulent i.e. Fatal. Other specie was Rough, non-capsulated and non-virulent. These were labeled as S-type and R-type bacteria. By injecting these bacteria in two separate rats, it was observed that S-type bacteria killed their host rat while R-type failed to harm their host rat. Later on S-type bacteria were killed with heat and they were injected in another rat along with some living R-type Bacteria. It was observed that the rat got pneumonia and got killed. On elimination of blood, it was found that the rat has got living S-type bacteria along with R-type specie. It was concluded by Griffth that:
“Live R-type bacteria received certain genetic material from dead S-type bacteria and ultimately transformed into live S-type.”
Economic Importance
Different type of bacteria not only causes diseases but some of the bacteria are also economically important for us. Some useful and harmful bacteria are as follows:
(a) Useful Bacteria
(i) Agricultural Bacteria
Bacteria living in the nodules over roots of Pea, Beans and other legumes convert atmospheric nitrogen into nitrate and Nitrite fertilizer, similarly other soil bacteria (generally called decomposes) convert dead plants and animal bodies into simpler compounds. Both above-mentioned bacteria increase soil fertility.
(ii) Medicinal Bacteria
Certain antibiotic drugs are also obtained from Bacteria.
(iii) Amino Acid and Protein Manufacturing Bacteria
Some important proteins and amino acids are also obtained from bacteria.
(iv) Symbiotic Bacteria of Alimentary Canal
Certain Symbiotic bacteria live in the alimentary canal of herbivorous where they produce live in the alimentary canal of herbivorous where they produce Cellulase enzyme required for the hydrolysis of cellulose into glucose.
(v) Industrial Bacteria
Bacteria perform different functions in different industries such as convertion of milk into curd and curd into cheese, ripening of tobacco leaves, tea fermentation, tanning of skins into leather etc.
(b) Harmful Bacteria
(i) Spoilage of Food
Every day a large quantity of food stuff like vegetables, fruits, meat, milk are spoiled by ferments released by bacteria.
(ii) Pathogenic Bacteria
A large number of diseases are caused by bacteria such as Furuncles, Sorethroat, Bronchitis, Pneumonia, Tuberculosis, Cholera and Typhoid etc. certain plant diseases are also caused by bacteria such as fine blight of apple and pear, back rot of cabbage , wild fine of tobacco.
Cyano
Bacteria (Blue Green Algae)
Nostoc
“It is a prokaryoticThallophyte belonging to the kingdom Monera.”
Occurrence
Nostoc is a fresh water algae commonly found in ponds, lakes, ditches and pools. Sometimes it also grows in damp soil.
Structure
Nostoc is a unicellular plant, a number of cells join to form long filaments. Each filament is few inches upto few feet long. A large number of filaments entangle in a gelatinous mass to form colony.
Each filament is beaded in appearance and is always unbranched. It is surrounded by a layer of Gelatin, which prevent filament from the rotting action of water.
Structure of a Single Cell
Each cell is rounded in shape with a double cell wall, the outer thicker gelatin coated wall is made up of cellulose and Pectine whereas inner layer is composed of cellulose only. Cell membrane is absent.
Cytoplasm is differentiated into two parts, the outer cytoplasm contains pigments like Chlorophyll, Xanthophyll, Phycocyanin etc mixed in the cytoplasm and not contained in membrane bounded Plastids. This outer coloured cytoplasm is called Chromoplasm. The inner cytoplasm is called Centroplasm. It is colourless and contains fragments of DNA.
True or complete membrane bounded nucleus is absent, instead of it incapient nucleus is present composed of fragments of DNA. There is no membrane bounded organelle in cytoplasm.
Heterocyst
In each filament there are some larger colourless cells called heterocyst are present. These cells convert atmospheric nitrogen into proteins and also serve to store food and multiplication.
Nutrition
Nostoc contains chlorophyll therefore it is capable to manufacture its own food material by means of Photosynthesis. Heterocysts also perform nitrogen fixation for filaments.
Reproduction
Like other blue green algae, Nostoc also reproduces asexually. Different methods of asexual reproductions are as follows.
(a) Hormogonia
Juctions of normal cells with Heterocysts are weak, therefore filaments often break at these points forming smaller fragments of filament, and each fragment is called Hormogonium. Hormogonium grows in length by means of mitosis and form new filaments.
(b) Akinete
In unfavourable conditions, some of the Nostoc cells become larger and thick walled containing reserved food. These cells are called Akinetes.
Each Akinete is surrounded by a thick layer, the outer wall is called Exospore and the inner wall is called Endospore. On return of favourable conditions, exospore bursts and endospore germinates to give rise to new filament.
= Kingdom Protista =
· This kingdom include all Eukaryotic unicellular or acellular living beings.
· These organisms may be aquatic or terrestrial. Free living organisms are found singly or in colonies.
· Some of the organisms are parasite and cause fatal diseases.
· Protistans may be Autotrophic having Chlorophyll, capable to produce their own food material while others are Heterotrophic and cannot produce their own food material.
· On the basis of mode of nutrition, Protistans are classified into two divisions:
1. Phylum Protozoa: Mostly Heterotrophic and
Motile.
2. Unicellular algae: All Autotrophic and
Sessile
Unicellular
Algae
Unicellular to Multicellular Organization
Unicellular algae are considered as the ancestor of multicellular plants. These plants have got miniature models and details of multicellular plants in a single cell and its organelles. On of the example is Chlamydomonas.
Chlamydomonas
Introduction
It is a unicellular green algae found in fresh water ponds, lakes, ditches and pools.
Nutrition
It is an autotrophic algae.
Structure
It is unicellular and solitary. Each single cell is capable to live by its own. Each cell is pear shaped with a pointed anterior end. Each cell is composed of following parts:
(i) Cell Wall
It is the outer most covering of the cell made up of cellulose and pectin. It is responsible for the distinct shape of the cell.
(ii) Cytoplasm
It is the inner ground substance of the cell which fills the inner space.
(iii) Chloroplast
It is single in number and cup shaped. It is large and occupies the major part of the cell lying towards the posterior end. It is filled with Chlorophyll.
(iv) Pyrenoid
It is large distinct protoplasmic body lying inside the Chloroplast. It functions to convert glucose into insoluble starch for storage.
(v) Nucleus
It is central and lies in the belley of chloroplast. It is complete i.e. surrounded by the nuclear membrane.
(vi) Stigma
Antero laterally, there is an orange –red spot on the cytoplasm called eye spot or stigma. It is sensitive to light.
(vii) Contractile Vacuole
These are two in number located at the anterior end at the base of Flagella. They are meant for excretion of water and respiration. They are pulsatile and osmo-regulatory.
(viii) Flagella
These are two cytoplasmic lash like structure meant for locomotion. Each flagellum arises from a granular body called Blepheroplast.
Reproduction
Chlomydomonas reproduce by two methods:
(a) A Sexual Reproduction
(b) Sexual Reproduction
(a) A Sexual Reproduction
A sexual reproduction takes place by following two methods:
(i) Zoospory
During favourable conditions especially at night, cytoplasm of chlamydomonas shrinks and separates from the cell wall. It condenses with the disappearance of flagella and vacuoles and divides mitotically to form 2 to 16 small uninucleated structures similar to the parent cell known as Zoospores. They are set free in water here each matures into a new chlamydomonas cell.
(ii) Palmella Stage
During unfavourable conditions the contents of chlamydomonas contract and collect in the centre where the cytoplasmic mass divides repeatedly to form large number of cells. These daughter cells are held together by a gelatinous mass. This is called Palmella stage. On return of favourable conditions daughter cells are released and develops into a complete chlamydomonas cell.
(b) Sexual Reproduction
During favourable condition, two chlamydomonas take part in sexual reproduction by means of gametes. These gametes are morphologically similar. Therefore there is no distinction of male and female gametes. Such gametes are regarded as positive and negative for identification purpose. Fussion of these gametes are called Isogamy and gametes are called Isogametes.
= Kingdom Fungi (Mycetes) =
· This kingdom includes Eukaryotic living beings.
· These Ekaryotes are multicellular or uni-cellular.
· There is no distinction of root, stem and leaf, such structures are called Thallus. Whole plant body or thalus is called Mycellium.
· Each Mycellium is composed of thread like structures called Hyphae.
· Each thaloid fungus is strickly Heterotroph and lacks chlorophyll.
· Reproduction is generally Asexual by means of spores but sometimes sexual reproduction by means of conjugation takes place.
· Hyphae are of two types namely:
Coencytic Hyphae ® having no cross walls between thecells example Mucor and Rhizopus.
Multicellular Hyphae ® having cross walls between the cells example Mushrooms.
· Fungi may be saprophytic or parasitic.
Rhizopus
Introduction
Rhizopus is a Eukaryotic Thalloid Fungi belonging to division Eumycophyta.
Occurrence
It is cosmopolitan i.e. found all over the world but especially in warm moist climate. It easily grows over decaying organic matter like bread, moist paper and leather etc.
Habits
It is saprophytic fungi which grows over decaying organic matter.
Structure
Plant body is called Mycellium composed of thread like hyphae. Each hyphae is coenocytic in nature i.e. lacks cross walls between the cells. It is composed of single row of cells with the inner connected cytoplasm, hyphae are unbranched and are of three types:
(i) Rhizpidal Hyphae
They are meant for attachment with substretum, absorption of moisture and food, secretion of enzymes for hydrolysis of food etc. They are branched.
(ii) Stolon Hyphae
They grow obliquely or along substratum and are meant for vegetative reproduction.
(iii) Aerial Hyphae or Sporangiophors
They grow upward and straight in air and are provided with sporangium. They are meant for spore formation and Asexual Reproduction.
Microscopically, each hyphae has got a boundary wall which is made up of a different type of cellulose called Fungal –cellulose. The tube like cairty of hyphae is filled with granular cytoplasm. It contains many nucleus freely moving with the flow of cytoplasm. Vacuoles are many containing Glycogen particles and Fats droplets.
Reproduction
Being a true fungi Rhizopus reproduces by means of following methods:
(a) A sexual Reproduction
(b) Sexual reproduction
(a) A Sexual Reproduction
Being a fungus, Rhizopus reproduces asexually be means of spores in favourable condition. In this reproduction, aerial branches arise which are called “Aerial Hyphae.” Some of the aerial hyphae become swollen at their tip and now known as “Sporangiophore”. In the swollen tip, nuclei along with a little dense cytoplasm began to collect. This cytoplasm and nuclei containing tip is called Sporangium. Soon after, fat globules containing vacuoles began to collect in Sporangium with separate the marginal part containing nuclei from the remaining hyphae. This marginal part is called capsule while the inner dome shaped non-nucleated portion is called Collumela.
Each nucleus of capsule is surrounded by a little cytoplasm and dries up to form spore. With increasing pressure of cytoplasm in Collumela, capsule burst to liberate spores.
The dry and light weight spores disperse in air and when they get any organic decomposing medium, germinate to give rise to a new Rhizopus Mycellium.
(b) Sexual Reproduction
In unfavourable conditions, Rhizopus also reproduces “Sexually”. In this reproduction two mycellia produce from two different sproes take part, these mycellia are morphologically similar but physiologically different. Such mycellia are called Hetero Thallus and sexual reproduction is regarded and Hetero Thallic Conjugation between positive and negative strains.
Explanation
When two hyterothallic hyphae come in contact they produce finger like outgrowths lying opposite to each other, these are called Progametangia. Nuclei along with little cytoplasm began to collect at the tips of these tubular progametangia which become swollen, later on a septum develops in each progametangium by which the swollen tip haivng nucleus separates and looses connection with the rest of the tube. This swollen tip is called Gametangium, its nucleus is regarded as Coenogamete, rest of the hollow tube of progametengium is called Suspensor. The two oppositely lying gamentangium fo the hyphae unite with each other and their intermediate walls get dissolve. The two similar looking coenogametes fuse to form zygote. The diploid (2n) zygote encloses itself in a cyst and becomes “Zygospore”.
Each zygospre has got an outer thick wall or Exosporium and an inner delicate membrane or endosporium. After some rest, exosporium bursts and the endosporium grows out to form a single and erect Hyphae the “Promycellium.” It develops a “Sporangium” without columella having haploid spores produced by which meiosis. Soon, Sporangium bursts and spores are set free. Half of the spores germinate to form positive strains and the remaining half give rise to negative strains of Rhizopus.
Economic Importance of Fungi
Fungi have a harmful and beneficial effects in many ways, these are given below:
Beneficial or Useful Importance
(i) Soil Fertility
Fungi decompose dead bodies of plants and animals and make the soil fertile. Leaf compost and manure is also made in the same way.
(ii) Fermentation
Some of the Saprophytic fungi release enzymes, they ferment different organic compounds into alcohol, acids, esters etc. For this purpose these fungi are used on industrial scale.
(iii) Food and Bakery
Some of the fungi, like Mushrooms are edible and are used throughout the world as food. Yeast is used in Bakery for fermentation of doe for bread and cakes.
(iv) Medicine
Some of the well known antibiotics are obtained from fungi like Penicillin, Neomycine, Streptomycine etc. Some of the fungi synthesize vitamin B.
Harmful Fungi
(i) Diseases
Some of the fungi cause human diseases like Athlete’s foot, Ring worm of skin, Candydiosis of tongue and throat, Moniliasis of lung etc.
(ii) Spoilage of Food
Most of the saprophytic fungi grow over edibles like vegetables, cooked food and fruits and spoil a large quantity per year.
(iii) Diseases of Crops
Stormy attack of fungi over crops destroy a number of crops, eg smut of wheat black powdery rust of cotton, Mildew etc.
Fungi also destroy cotton, wool, leather and wood, paper etc.
= Kingdom Plantae =
· All Eukaryotic, multicellular and Autotrophic plants are included in Kingdom Plantae.
· They have got cellulose made cell wall and differentiated body parts in many. Few exceptions are also present
FIGURE (CHART)
Stigeocolonium
Introduction
It is a Eukaryotic, Thallophytic filamentous algae.
Habitat
It is found in stagnated fresh water like ponds, lakes, pools and ditches. It is also found in slow running streams.
Habits
It is a Thallophyte belonging to the class Algae. Due to its green colour it is kept in the family chlorophycese. It is Autotrophic plant.
Structure
Plant body is called “Thallus” which is undifferetiated into roots, stem or leaf. Thallus is composed of row of cells called filament. Filaments are of two types i.e. Heterotrichous; one of the filament is attached with the substratum while the other (branch) is fibrous and grows vertically in water, these branches or filaments are called Protstate and Erect Branches respectively, Both type of filaments are surrounded by mucilagenous layer. Prostatic branches grew diffusely and Psendo parenchymatons whereas Erect branches terminate on hyaline hairs.
Structure of Each Cell
Each cell is rectangular i.e. longer than the breadth. It is surrounded with a cell wall. Cytoplasm forms a thin film with the inner lining of cell wall. A single large girdle like chloroplast is found in the middle of the cells having many Pyrinoids. A complete nucleus is present in the centre suspended with cytoplasmic strands.
Reproduction
Stigeoclonium reproduces by two methods:
(a) A sexual Reproduction
(b) Sexual reproduction
(a) A Sexual Reproduction
In each cell of prostate branch, four to eight Zoospores are produced mitotically. Each zoospore is Quadriflagellate i.e. bears four flagella. After liberation, each zoospore grows to form a new plant.
(b) Sexual Reproduction
In the cells of porstate branches sexual cells or gametes are produced. These gametes are usually Biflagellate. They are similar in morphology and physiology, therefore regarded as Isogametes. Two isogametes fuse to form Zygote, fusion of these isogametes is called Isogamy.
Zygote usually after a period of rest germinates Meiotically to form haploid quadriflagellate four Zoospores. Each zoospore after liberation grows into a new thallus.
Ulva
Introduction
It is a multicellular, Eukaryotic thalloid algae commonly known as Sea-Lettuce.
Habitat
Ulva is a marine algae which grows attached to rocks in intertidal pools.
Habits
It is a thalophytic algae which cannot be differentiated into root, stem or leaf. Being an algae, it is autotrophic in nature.
Structure
Each thallus is a blade like wrinkled structure almost 20 to 30 cm in length. The lower part of thallus remains attached with rocks by means of “Hold Fast” having elongated cells.
Thallus is composed of two layers of cells i.e. outer epidermal layer of cells containing chlorophyll and an inner layer of cells i.e Medulla serving as storage tissue.
Reproduction
It is of two types namely:
(c) A sexual Reproduction
(d) Sexual reproduction
(a) A Sexual Reproduction
It takes place by means of quadriflagellate zoospores produced by asexual diploid (2n) plant called Sporophyte. Zoospores are produced in all cells of plant by means of Meiosis. Usually each cell produces 8 – 16 zoospores. Each zoospore on germination gives rise to a new haploid (n) plant.
(b) Sexual Reproduction
The haploid plants thus produced are called Gametophytes. Two similar looking gametophytes are produces. They are also morphologically similar to Sporophyte except their number of chromosomes. Two Isomorphic gametophytes are regarded as negative and positive strains.
Both gametophytes produce haploid gametes, these gametes are smaller than the zoospores and Biflagellate. Similar looking negative and positive gametes or isogametes fuse to form a quadriflagellate zygote i.e. isogamy takes place.
The zygote after rest and repeated divisions gives rise to a new diploid sporophytic plant.
Alternation in Generation
Definition
“The phenomenon in which a plant completes its life cycle in two phases i.e. haploid gamotophyte and diploid sporophyte which come in an alternate manner is called alternation of Generation.”
Explanation
In Ulva Sporophyte bears 2n i.e. Diploid Chromosomes which is 26. This plant reproduces by means of spores produced by means of Meiosis, Each spore bears haploid (n) or 13 chromosomes. On germination spores give rise to Gametophyte plants which are similar to Sporophyte in morphology but differ in the number of chromosomes.
Gametophytes produces isogametes which fuse to form zygote having Diploid (26) chromosomes. Zygote gives rise to zoospores which germinate to form Diploid Sporophyte and thus whole cycle is repeated.
In Ulva, Sporophyte and Gametophytes are of the same morphology therefore, life cycle is called Isomorphic alternation of Generation.
Marchantia
Occurrence
Marchantia is a land plant generally found in moist shady and cold areas.
Habits
Marchantia is a Bryophute live wort. Plant body is Thalloid in nature without distinction of root, stem and leaf. It contains chlorophyll, therefore it is autotrophic in nature.
Structure
Plant body is Thalloid i.e. no distinct roots, stem and leaves are found but Dorsal and ventral surfaces are distinct. Ventral surface bears unicellular Rhizods while Dorsal surfaces bears a Pseudo Midrib. Rhizoids are meant for absorption and fixation of plant. Ventral surface also bears chloroplast and air chambers for exchange of gases.
Reproduction
Marchantia reproduces by three methods:
(a) Vegetative Reproduction
(b) A sexual Reproduction
(c) Sexual reproduction
(a) Vegetative Reproduction
It takes place by means of Gemmae. On each plant, small cup shaped structures are produced along with the Midrib known as Gemma cup. In each gemma cup a large number of microscopic Gemmae are produced, each gemma detaches from the cup and germinates to form a new plant.
(b) A Sexual Reproduction
Sporophyte of Marchantia is a small atypical plant consisting of three parts i.e. basal Fout, stalk like Seta and swollen Capsule. Within capsule a large number of spore mother cells are present these Diploid cells divide meiotically to produce haploid tetrads of spores. On maturation, capsule bursts and spores are set free. Each spore germinates to give rise to a new Gametophyte plant.
(c) Sexual Reproduction
The basic or dominant phase of the life cycle of Marchantia is sexual or Gametohytic. Plants are Dioecious i.e. Male and Female plants are separate.
Male plant produces an erect branch called Antheridiophore while female plant produces Archigoniophone. Both of these branches bear Male and Female receptacles respectively.
Male receptacle is disc shaped and bears on its upper surface Male reproductive organs called Antheridia. Each anteridium is club shaped with a stalk and capsule. Each capsule bears a large number of haploid Antherozoid mother cells, which give rise to male gametes or biciliated sperms.
Female receptacle is star shaped and bears on its lower surface inverted flask shaped Archigonium. They belley of the flask or venter contains a single large female gamete of egg having haploid chromosomes.
Fertilization
Biciliated sperms escape after maturation when antheridium bursts. They swim towards archigonium and enter through the neck to reach the egg cell in venter. One of the sperm fuses with the egg i.e. fertilization takes place. After fertilization, zygote encloses itself in a thick wall and becomes Oospore.
After sometime, oospore germinates over the female receptacle as a parasite and gives rise to a Diploid Sporophyte plant.
Alternation of Generation
Marchantia shows a distinct alternation of generation. The dominant place of life is haploid Gametophytic phase alternating with indistinct Diploid Sporophytic phase for a short time.
As male and female gametes as well as Male and female plants (Gametophytes) are totally different from Sporotphyte, thereofe this life cycle may be regarded as Heteromorphic, Heterogamous life cycle.
Seed
Seed is a reproductive part of Phanerogams as a result of fertilization of ovule of the ovary. It germinates to give rise to a new plant of the same specie.
Types of Seed
Seeds are of two types:
1. Dicotyledonous or Dicot Seeds
2. Monocotyledonous or Monocot Seeds
1. Dicot Seed
Definition
“The seeds having two cotyledons in their embryo are called Dicot Seeds.”
Examples
Examples of Dicot seeds are Pea, Bean, gram and Mango.
Parts of a Dicot Seed
Different parts of a dicot seed are as follows:
(i) Seed Coat
it is the outer protective covering of the seed. It is composed of two layers; the outer, thicker, tough and sometimes coloured and brittle layer is called Testa. The inner, thin, and soft layer is called Tegmen. Both layers are usually fused together. In certain seed like Castor, Testa is coloured having markings on it and an outgrowth called Caruncle. Hilum is a mark over testa which shows the site of attachment of seed with the Placenta. In the centre of hilum or somewhate nearer to it is a minute hole in the testa called Micropyle through which water and air enters into the seed.
(ii) Embryo
After removal of seed coat, the inner structure appears called “Embryo.” It is composed of two fleshy structures called Cotyledons and a small axis. In castor-oil seed cotyledons are thin and leaf like and overlapped fleshy Endosperms which store the oil and fats. Cotyledons and endosperms serve to store food for seedling. The seeds having endosperms are called Albuminous or Endospermic seeds while those which are devoid of them are called Non Endospermic.
Axis is composed of two parts; an outer Radicle which protrudes out from the gab between the two cotyledons and an overlapped and hidden Plumule which lies between the two cotyledons. Plumule is feather like in structure which forms the shoot while radicle gives rise to root on germination.
2. Monocot Seed
Definition
“The seed having one cotyledon in its embryo is called Monocot seed.”
Examples
Examples of Monocot seed are Rice, Maize and Wheat etc.
Parts of Monocot Seed
Structure of a monocot seed is as follows:
(i) Seed Coat and Fruit Wall
In maize grain, Pericarp of fruit and seed coat are fused together forming a single outer protective coat. In such seeds, hilum and Micropyle are absent. Such combined seed and fruits are generally called grains.
(ii) Endosperm and Cotyledon
A single thin layer of cells called Epithelium obliquely divides the grain into unequal parts, the upper larger food and fat containing portion is called Endosperm and the smaller shield shape lower portion is called Scutellum representing the cotyledon. Embryo lies in the Scutellum which is composed of upper plumule and lower radicle. Both these structures re covered with cap like protective sheaths called Coleoptile and Coleorhiza respectively.
Germination
Definition
“Wakening of a dormant sleeping embryo in particular condition to give rise to a seedling is called Germination.”
Types of Germination
Germination is of following three types:
1. Epigeal Germination
In this type of germination, the part of axis just below the cotyledons and above the rodle, commonly known as Hypocotyle elongates rapidly and carries the cotyledons above the soil. In such cases, cotyledons are usually thin and leaf like. They turn green and start carbon assimilation. In other cases, they remain fleshy and soore wither. For example Castor oil seed, gound, Sunflower and 4°clock plant.
2. Hypogeal Germination
In this type of germination, the parts of axis above the cotyledons and below the plumule, commonly called Epicotyle elongates rapidly due to which cotyledons remain inside the soil. In this condition, cotyledons are generally fleshy and non green. They supply nutrition to the rapidly growing seedling during germination and soon become dry. Examples are Pea, Maize and Gram.
3. Viviparous Germination
In the especial type of germination, seeds usually grow within the fruit and nourished by the fruit and parent plant. Radicle of the seed becomes elongated, stouter and swollen. The seedling becomes heavier and gets separated from the plant. It falls vertically down in the mud or marsh where radicle gets embeded and seedling starts to grow into a plant. Examples are Mangrooves like Rhizophora and Coconut.
Parts
of an Angiospermic Plant
A typical angiosperm is divided into two parts:
1. Vegetative Parts
2. Floral or Reproductive Parts
1. Vegetative Parts
These are the parts which usually do not take part in reproduction. However they form the mass of an Angiosperm. These parts are:
(i)
Root
(ii)
Stem
(iii)
Leaf
2. Reproductive Parts
The parts of plant, which usually take active part in the sexual reproduction of the plant, are called Reproductive Parts. These are:
1.
Flower
2.
Fruit
3. Seed
(i) Root
Root is the underground part of the plant, generally non-green and positively Geotropic (grows towards earth and Negatively Phototropic (grows away from the light). It is actively Hydrotropic i.e. grows towards water or moisture.
Types of Roots
Roots are of two types:
(a) Tap Root which develops from the radicle of a seed.
(b) Adventitious Root which develops from any part of the plant other than the radicle i.e. from stem, branch or leaf.
Functions
· Fixation of plant to the substratum.
· Absorption of water and minerals.
· Conduction of absorbed water to the stem.
· Storage of food sometimes.
(ii) Stem
It the aerial part of the plant which develops from the plumule of the seed or sometimes from the stem cutting. Stem gives rise to branches which develop from the axillary bud. It is positively Phototropic, negatively geotropic; it is exogenous in nature. Stem always possesses nodes and internodes and a terminal bud at its tip. It gives rise to branches, leaves and buds (vegetative and floral).
Functions
· Support to the branches, leaves and other structures.
· Conduction of water from roots to the leaves.
· Spreading of leaves to the sunlight.
· Conduction and sometimes storage of food.
(iii) Leaf
These are outgrowths of nodes of the stem, generally flat and green in colour. They contain green pigment called Chlorophyll and are provided with an axillary bud in its axil.
Fuctions
· Support to branches, leaves and other structures.
· Conduction of water from roots to the leaves.
· Spreading of leaves to the sunlight.
· Conduction and sometimes storage of food.
(iii) Leaf
These are outgrowths of nodes of the stem, generally flat and green in colour. They contain green pigment called chlorophyll and are provided with an axillary bud in its axil.
Functions
· Preparation of food by means of photosynthesis.
· Transpiration of water.
· Thermoregulation (control of plant’s temperature)
Modification
of Stem
Modification
“The phenomenon in which any part of the plant changes its morphology to perform certain specialized function is called Modification.”
Stem (or branches) of a plant sometimes modify to perform storage of food and water. These modification are as follows;
Underground Modifications of Stem
In some plants, under unfavourable conditions the stem develops underground and remains dormant. However at the approach of favourable conditions they give aerial shoots and strike flowers. Such dormant growing sub soil stems are called under ground modified stems.
Functions & Reasons for Modification
1. Storage of Food and Water
Plants prepare excess amount of food and transfer it to the underground stem for storage purpose for draught i.e. unfavourable season.
2. Perennation
Plants survive from bad season and may live for four years by means of underground modifications.
3. Vegetative Propogation
Underground stem gives off lateral branches which strike roots and when separated from the parent plant, produce new plants thus increasing the number.
Types of Underground Stems
Following are the different types of underground stems:
1. Rhizome
· It is an underground prostrate stem.
· It always grows horizontally beneath the surface of soil.
· Due to heavy storage of food, it is thick and fleshy.
· It bears adventitious roots on its under surface.
· It is provided with distinct nodes and internodes.
· From the nodes scaled leaves arise protesting the axillary buds.
· It also develops lateral branches from axillary buds.
· During favourable conditions, it produces aerial shoots from axillay and terminal buds.
· Examples are Ginger, Canna and Banana.
2. Corm
· It is an underground stem, which grows vertically.
· Due to heavy deposition of food, it is somewhat rounded and fleshy.
· Terminal bud lies apically.
· Distinct circular nodes and internodes are also present.
· Nodes bear scale leaves for protection of axillary buds.
· Adventitious roots are produced from the underground surface.
· Examples are Colocasia and Gladiolus.
3. Stem Tuber
· These are condensed, fleshy and swollen tips of underground branches which arise from the axillary buds of an aerial stem.
· Underground branches develop from the axil of withered scale leaves.
· The swollen tip i.e. “tuber” acquires a rounded shape but generally the shape is ill-defined.
· Each tuber is provided with “eyes” which consist of nodes, scar of scale leaf and axillary bud.
· In unfavourable season aerial shoot dies off and the underground tubers survive which give rise to new plants on retum of favourable conditions.
· Examples are Potato, Helianthes tuberosus.
4. Bulb
· These are condensed and reduced type of U.G. stem.
· In this modification, stem reduces to a disc.
· Disc is provided with a tuft of fibrous adventitous roots on its under or ventral surface.
· The upper or Dorsal surface of disc has got extremely reduced nodes and internodes forming a convex surface.
· Crown of the scale leaves develops from the upper convex surface having axillary and terminal buds.
· Buds grow into aerial shoots during favourable conditions.
· Scale leaves are fleshy due to deposition of food.
Types of Bulbs
Bulbs are of two types:
(a) Tunicated Bulb
In this bulb, scale leaves are arranged in a concentric manner and the whole bulb is surrounded by a thin, dry and papery scale known as Tunic. Examples are Onion and Lilly.
(b) Scaly Bulb
In this bulb, scale leaves or scales are arranged in an “Imbrieate fashion” i.e. overlapping each other. Each scale is separately covered by a dry cover. Examples are Tube rose and Garlic.
Aerial Modifications of Stem
Axillary buds normally grow into vegetative or floral branches. In some plants, these axillary buds modify extremely to give rise to specialize structures, which perform definite functions. These structures are called aerial modifications of stem. They are as follows:
1. Thorn
· It develops from an axillary or a terminal bud.
· In this modification, the branch becomes a sharp, hard pointed structure.
· This dry looking sharp structure i.e. Thorn may has got leaves or even flowers at its nodes.
· This modification is meant for defence and to reduce the rate of transpiration.
· Examples are Duranta, Athagi and Carissa.
2. Tendril
· It is also a modification of axillary or terminal bud.
· In this modification, bud grows into a long, thread like sensitive structure which twins around any hard object when comes in contact.
· This modification is found in weak stem climbers.
· Tendril is meant for support.
· Examples are Passion Flower and bitter guord.
3. Leafy Stems
In xerophytes (i.e. desert plants) leaves soon wither or modify into spines to reduce the rate of transpiration. Due to modification, leaves become unable to manufacture food. In such cases, stems become flat, green and leaf like. Such stems are called Leafy Stems. They perform the functions of leaves i.e. manufacturing of food, transpiration and respiration. These leafy stems are of two types;
(a) Phylloclade
· It is a modified main stem i.e. of unlimited growth.
· It is flat, green and thickly covered with cuticle.
· It has got many nodes and internodes.
· Nodes bear modified leaf spines and axillary buds.
· It performs functions of leaf as well as storage of water and food.
· Examples are Opuntia, Euphorbia.
(b) Cladode
· It is a modification of axillary branch.
· It is flat, green and thin, greatly resembling a leaf.
· It is composed of a single internode.
· It is always axillary in position.
· Examples are Asparogus and Ruscus.
4. Bulbil
· It is a modified axillary bud.
· It is thick and fleshy and may store food.
· It soon falls off and grows into a new plant.
· Sometimes it develops a crown of leaves before falling.
· Bulbil is meant for vegetative reproduction.
· Examples are Oxalis and Pineapple.
Modification
of Leaf
“The phenomenon in which any part of the plant changes its morphology to perform certain specialized function is called Modification.”
Sometimes whole leaf or a part of it modifies into a specialized structure to perform some important function. These modifications are as follows:
1. Leaf Spine
· It is a modification of whole leaf or a partial modification of some of its part.
· In this modification, leaf modifies into a sharp dry and pointed structure.
· In some plants, ptipules, leaf margin or leaf apex becomes sharp and pointed i.e. spine.
· This modification is meant for protection or to reduce the rate of transpiration.
· Examples are Opuntia, Date palm and Barnerry.
2. Leaf Tendril
· It is the modification of whole leaf or part of it.
· In this modification, whole leaf or part of it becomes elongated thread like sensitive structure called Tendril.
· Tendril twins around any hard object when comes in contact.
· It is usually found in weak stem climbers.
· This modification is meant to provide support to the weak stem.
· Examples are Pea, Gloriosa and Nastertium.
3. Scale Leaf
· It is a modification of whole leaf.
· In this modification leaf becomes non-green, thin and membranous.
· Sometimes scale leaves are succulent and fleshy for storage of food.
· Scale leaves are always Sessile.
· Dry scale leaves are meant to protect axillary bud.
· Examples are Ginger, Garlic, Onion and Lilly.
4. Phyllode
· It is a modification of compound leaf.
· In this modification, leaflets of the compound leaf are deciduous and soon fall off.
· The rachis or petiole of the leaf gradually becomes flat, green and leaf like.
· This flattened rachis is called Phyllode.
· Reason for this modification is preparation of food and to reduce the rate of Transpiration.
· Examples are Parkimsonia and Australian Acacia.
= Phylum Hemichordata =
· It is a small phylum containing few animals.
· Animals are generally called Acorn Worms which are found buried in mud or below stones at sea shores.
· Body of the animal is composed of Proboscis, Collar and Trunk.
· Proboscis lies anterior, it is muscular, conical and provided with Cilia.
· Proboscis secretes mucus with which food particles get attached and are carried to the mouth of Ciliary movement.
· Mouth lies ventrally at the junction of proboscis and collar.
· Respiration is by means of gills found laterally on both sides of anterior 1/3rd of long trunk.
· Digestive system is complete.
· Excretion is by means of Nephridia.
· Sexes are separate in fertilization of eggs is exterior.
· Fertilized eggs hatch into Tornaria larva.
· Example is Belanoglossus.
= Phylum Chordata =
Animals of this phylum are the most developed according to the Evolutionary point of view. They have the most advanced body organs. These animals may differ in their morphology but share some common features, which are as follows:
1. Notocord
During development an ectodermal invagination takes place dorsally in these animals which is called Notocord. It is slender and rod shaped. In some animals it may persist during embryonic period while in others it is persisted or may organize into vertebral column.
2. Hollow Dorsal Nevous System
Nervous system is well developed and lies dorsally. It is hollow internally forming chambers or ventricles.
3. Gill’s Clefts
During development, al these animals bear Pharyngeal gill’s Clefts on both sides. These gill’s Clefts soon disappear after combination of development but in some animals they persist and convert into respiratory organs.
4. Paedomorphosis
Chordates are developed from Auricittaria Larva of Echinoderms. According to some workers, this larva was non-motile and due to Neoteny developed reproductive organs. Soon, reproduction started in these larva and the off springs became Adults having advanced characters. This whole phenomenon is called Paedomorphosis.
Classification
of Phylum Chordata
Phylum Chordata is divided into following three sub Phyla;
1. Urochordata
2. Cephalo Chordata
3. Vertebrata
1. Sub Phylum Urochordata
· Animals are generally called Tunicates.
· They are marine and Sessile, they are generally found attached with the rocks, bottoms of ships and boats.
· Larva are actively motile and called tadpoles.
· Adult animal is sessile, rounded having two openings at different places. These openings are called Siphons.
· Water enters through Buccal or Incurrent Siphon and passes out through Atrial or Excurrent Siphon. During passage through gills, O2 is absorbed and CO2 is released.
· Animals are fitter feeders and feed upon organic matter and particles entrapped during passage of water.
· Sexes are separate and animals are oviporous.
· Fertilization is external.
· Heart is single chambered.
· Tadpole larva bears nerve cord and Notocord in its tail.
· Notochord is absent in adults, similarly the tail.
· Example is Ascidia.
2. Sub Phylum Cephalochordata
· Animals are generally called Acorn Worms.
· They are marine and found in sand along shores.
· Body of the animal is spindle shaped, it is small up to 5cm length and devoid of head and neck.
· Sensory organs like eyes and ears are also absent.
· Brain is absent but dorsal nerve cord is present.
· Digestive and circulatory systems are complete.
· Excretory organs are nephridia.
· Respiration is by means of gills.
· Animals have Nocturnal habits and sleep during day time.
· Dorsal and Caudal fins are present for swimming.
· Example Amphioxus.
3. Sub Phylum Vertebrata
· It is the most developed and highly evolved Sub Phylum.
· Animals are cosmopolitan i.e. found all over the world in aquatic and terrestrial habitats.
· Notochord, Pharyngeal gills and hollow nervous system are the characteristic features.
· Notochord is found in embryonic life but may be present and persistent in some species in adult life.
· Notochord is soon replaced by Vertebral Column during development, which may be bony, or Cartilagenous.
· Nervous system is composed of Brain and Spinal cord, both are hollow internally. Brain is enclosed in a skull.
· Locomotary organs are two pairs of limbs called fore and hind limbs or pectoral or Pelvic limbs.
· Circulatory system is composed of closed vessesls and heart.
· Excretory organs are a pair of kidneys.
· Skeleton is internal (Endoskeleton) and made up of cartilage or bones.
· Sensory organs are well developed.
· Sexes are Separate, animals are oviparous or viviparous.
· Fertilization is internal or external.
Types of Sub Phylum Vertebrata
Sub Phylum Vertebrata is divided into following seven classes.
(i) Class Agnatha or Cyclostomate
(ii) Class Chondrichthyes
(iii) Class Osteichthyes
(iv) Class Amphibia
(v) Class Reptelia
(vi) Class Aves
(vii) Class Mammalia
(i) Class Agnatha or Cyclostomate
· Animals are marine or found in fresh water.
· Body of the animal is elongated and slender.
· Notochord is persistent up to adulthood therefore vertebral column is absent.
· Mouth is ventral, rounded and modified into sucker.
· Jaws are totally absent.
· Limbs are absent and locomotion is carried out by means of too and fro movement of body.
· At the aterior end of body above the mouth, a single nostril is present.
· Respiration is by means of 7 pairs of internal gills.
· Skin is smooth and scales are absent.
· Mouth is provided with teethed tongue for scraping of flesh of other animals.
· Excretion is by means of kidneys.
· Sexas are separate and fertilization is external.
· Dorsal and Caudal fins are present.
· Excretory and Genital openings are separate.
· Example : Sea Lamprey
FIGURE
(ii) Class Chondricthyes
· This class is also called Elasmobranchiata.
· Animals of this class are marine, few in fresh water.
· Skin is smooth, few species have placoid scales.
· Body is elongated and spindle shaped. Neck, thorax and abdomen is undifferentiated.
· Endoskeleton is made up of cartilage.
· Limbs are two pairs in number, which are modified into Pectoral and pelvic fins.
· A prominent dorso-median and small ventral fins help the body during swimming to gain stability and equilibrium.
· Tail is also modified into Caudal fin, It is hetero cercal i.e. divided into two unequal parts.
· Conical head bears a slit like ventral mouth equipped with similar teeth. Animals are Poikelotherms or Cold blooded.
· Respiration is by means of 5 pairs of internal gills, which open to the exterior by means of gill’s clefts.
· Circulatory system is of closed type provided with 2 chambered heart.
· Nervous system and sensory organs are well developed especially the sense of smell. Eyes are devoid of eyelids.
· Nostrils are two, lying anterio-ventrally which are internally closed and are meant for smelling.
· Sexes are separate, Fertilization is internal, and females are oviparous. Some species are ovo-viviparous.
· Some of the deep sea animals are dorso-ventrally compressed.
· Examples are Sharks, Torpido, Dog Fish and Kite fish.
(iii) Class Osteichthyes
· This class is also called Teleostomi.
· Animals are aquatic and evenly distributed in fresh water and Marine water.
· Endo skeleton is made up of bones therefore animals are called Bony fishes.
· Body is of variable shapes i.e. spindle shaped, elongated, dorso-ventrally compressed.
· Body is generally covered with scales, sometimes scales are absent.
· Limbs are modified into pectoral and pelvic fins, Tail is also modified into Caudal fin which is homo cercal i.e. equally divided.
· Body is supported with Dorso-median and Ventral fins.
· Respiration is by means of internal gills covered with a bony shield like flap called Operculum.
· Circulatory system is closed and heart is two chambered.
· Animals are Poikilotherms or cold blooded.
· Nervous system and sensory organs are well developed.
· Some fishes bear air bladder to make body lighter.
· Sexes are separate and female is oviparous.
· Fertilization is external.
· Examples are sea horse, Rohu, Salmon and Trout.
(iv) Class Amphibia
· Animals of this class live in both (aquatic and terrestrial) habitats.
· Skin of these animals is loose, smooth and Glandular, it is kept moist by mucus secretion.
· Body is supported with two pairs of longitudinal limbs namely fore limbs and hind limbs.
· Limbs are provided with digits but nails are absent.
· Body is composed of head and undifferentiated trunk.
· Skeleton is composed of long and flat bones.
· Nervous system and sensory organs are very well developed.
· Mouth is slit like and antero-ventrally located. It is provided with similar teeth and anteriorly fixed bifid tongue.
· Circulatory system is closed and heart is initially three chambered, which becomes five chambered on maturation.
· Mode of respiration is dual i.e. through skin and by means of lungs. Some of the animals bear external gills.
· Animals are Poikilotherm i.e. cold blooded.
· They show seasonal escape i.e. hybernation in winter and Aestivation in summer to avoid extremes of weather.
· Animals may be tail-less (order Anura) or bear strong tail (order urodela) as a swimming organ.
· Sexes are separate, female is oviparous and lays eggs in water.
· Fertilization is external and in water, young ones show Metamorphosis.
· Examples are Frog, Toad, Salamender and Nocturus.
(v) Class Reptilia
· Animals are terrestrial and well adapted for land.
· They are Poikilotherms.
· Skin is dry and provided with scales.
· Skeleton is internal and made up of bones.
· Respiration is by means of lungs only.
· Circulatory system is closed and heart is three chambered in many.
· Nervous system and sensory organs are well developed. External ears are absent.
· Mouth is slit like and anteriorly located. It is provided with similar teeth and anteriorly fixed bifid tongue.
· These animals show seasonal escape i.e. hybernation in winter.
· Limbs are 4 in number, muscular and provided with digits having nails or claws.
· Tail is prominent and muscular.
· Sexes are separate, females are oviparous or ovo-viviparous in some species.
· Egg is covered with hard shell and contains large amount of yolk, such eggs are called Polylicethal.
· Eggs hatch into young ones completely resembling the adults.
· Eggs are provided with a protective membrane internally called Amnion and therefore animals are regarded as Amniotes.
· Examples are Lizards, Crocodile, Turtle and Tortoise, snakes etc.
(vi) Class Aves
· These animals arise from the reptiles and therefore are terrestrials.
· They are typically homoiotherms or warm blooded i.e. can regulate their body temperature.
· Body is covered with feathers, which are actually an alternation of reptilian scales.
· Body is divided into head, neck, thorax and abdomen.
· Body is provided with two pairs of limbs, forelimbs are modified into flat, wide wings which are the organs of flight (in many).
· Hind limbs are muscular, externally and distally covered with scales. They are meant for walking and running.
· Hind limbs are also provided with digits having nails. They are of various shaped adapted for walking, grasping, scratching and swimming.
· Vertebral column is composed of five types of vertebrae namely carvical, thoracic, lumbar, sacral and caudal vertebrae respectively. Lumbar and sacral vertebrae unite to form Synsacrum. Thoracic vertebrae are attached with ribs and Sternum.
· Jaws are modified into beak and bill of various types.
· Skeleton is mostly composed of hollow bones.
· Respiratory organs are lungs haring air sacs.
· Circulatory system is closed, heart is four chambered and oxygenated blood is completely separated from deoxygenated blood.
· Windpipe is provided with a special sound-producing chamber that is called Syrinx.
· Nervous system is sensory organs re very well developed.
· Sexes are separate, female is oviparous and fertilization is internal.
· Egg is Polylicethal and provided with amnion.
· Examples are Eagle, Crow, Sparrow, Parrot and Pigeon.
(vii) Class Mammalia
· It is the most evolved class of animal kingdom.
· Most of the animals are terrestrial, some species live in water.
· Animals are homoiotherms, i.e. warm blooded.
· Skin is provided with hair, sweat and sebacious glands.
· These animals are provided with Mammary Glands which secrete milk for nourishing young ones.
· Mouth is provided with different types (four types usually) of teeth.
· Respiration is by means of lungs.
· Heart is four chambered and oxygenated blood is kept separated from the deoxygenated blood.
· Skeleton is internal and composed of long and flat bones.
· Limbs are four in number, provided with digits and nails.
· Vertebral column is composed of cervical, Thoracic, Lumbar, Sacral and Caudal (Coccigeal) Verterbrae.
· Ribs are present and attached with Thoracic vertebrae.
· Nervous system and sensory organs are highly developed.
· Body is divided into head, neck, Thorax and Abdomen.
· Thorax is separated from abdomen by means of Diaphragm.
· Sexes are separate, fertilization is internal and females are viviparous.
· Young one usually develops in the uterus of female and remains attached with it by means of Placenta. Embryo is surrounded by Amnion and Chorion membranes during development.
· Animals bear external ears and eyelids.
· Mammalia is divided into three sub classes:
(a) Prototheria or Egg laying Mammels – eg: Duck nill platypus
(b) Metatheric or Pouched Mammels – eg: Kangaroo
(c) Eutheria or Placental Mammels – eg: Human, Squerrel, cat, Dog, sheep etc
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