Describe Fungi. Discuss structure of thallus, nutrition and reproduction in them

Fungi are thallophytes of chlorophyll less non vascular plants that live parasitically or saprophytically and reproduce by spores. Branch of botany which deals with fungi is called Mycology. Study of disease caused by fungi are called plant pathology. Fungi are found every where. They have no chlorophyll and may be saprophytes, parasites or symbionts. Some fungi are aquatic. Some are terrestrial. They occur in soil. Some live in tissues of plants and animals. Fungi can grow on our food stuffs like bread, jams, pickles and fruits. They are also present all the time in air.

Vegetative structure of Fungi:

Fungi consists of network of branched filaments called hyphae. Entangled mass of hyphae is myceliym. Hyphae may be segmented or non segmented. Some fungi like yeasts (Saccharomyces) and Syachtrium lack mycelium.

Cell wall of mycelium is made up of chitin or fungal cellulose along other substances.

Chief food reserves are glycogen and oils. Fungal cells contain cytoplasm, nuclei and vacuoles. Mycelium of lower fungi is aseptate and coenocytic where as of higher fungi it is septate and cell may be uni, bi or multi nucleate.

Mycelium may be of following kinds.

(1) Piectenchyma:- When the fungal mycelium is compactly woven to form a pod like tissue called as plectenchyma. It is of two types prasenchyma in which hyphac of the mass retain their individuality and do not fuse and pseudoparachma in which hyphare are completely fused to each other and lost their individuality and the whole mass looks like the parenchyma of higher plants.

(2) Sclerotia:- In this case the interwoven hyphac of mycelium become compact that the mass becomes rounded and cushion like and is know as sclerotia.

 (3) Rhyzomorph:- These are complex structures in which hyphac grow side by side. They are dark brown gelatinous and thick. They sometime resemble the finer roots of a tree.

Nutrition:- There is lack of chlorophyll in fungi hence they are unable to synthesize food. They are heterotrophic in their mode of nutrition and they get food from external source. Thus they live either as parasites or saprophytes. Fungi that get their food from dead organic material are called sabrophytes and the fungi which obtain their prepared food from living plants or animals are called parasites. The living beings on which the fungi parasitize are called hosts. Some fungi grow in association of other plants and are mutually benefited and this process is called symbiosis.

Reproduction:- Reproduction in fungi takes place by vegetative reproduction, asexual method and sexual method.

(1) Vegetative Reproduction:- It takes place by

(i) Fragmentation:- Hyphac break up into two or more pieces due to some external force and each of them develops into new one.

(ii) Fission:- Some unicellular fungi like yeast and bacteria reproduce by fission. The vegetative cell elongates and divides into two daughter cells by constriction or transverse wall.

(iii) Budding:- The parent cell buds off new cell which separates from parent cell and develop into new individual. Eg. Yeast cells.

(iv) Sclerotia:- This is modification of mycelium. It is hard, resting storage object. It also serves as a means of perenvation and vegetative propagation on return of favourable conditions it germinates.

(2) Asexual Reproduction:-

It takes place by several types of spores as under:

(i) Motile Zoospore:- Motile zoospores may be uni or biflagellate pear shaped sporangium eg. Albugo and syachyterium.

(ii) Conidia:- These are non motile spores produced exogenously by constriction at the ends special hyphal branches called conidiophores. They may be produced singly (eg. Phythinum, phytophthora) or in chains (eg. Aspergillus & Penicillium).

(iii) Oidia:- Some fungi like mucor the hyphae forming mycelium become divided by transverse walls into large number of short segments each of which is capable of germinating and developing into a new plant. These segments which remain united in chains become free from each other and are known as oidia.

(iv) Chlamyolospores:- They are produced like that of oidia but they differ from the latter being thick walled and coloured black or brown. They may be terminal or produced at irregular intervals along the hyphae.

(v) Spores:- They are simple reproductive units usual unicellular and with certain food reserve. In higher fungi like ascomycetes and basidiomycetes ten spores-asporpores and basidiospore, are produced.

(3) Sexual Reproduction:- In fungi like other organisms sexual reproduction takes place by the union of two compatible nuclei and consists of three phases.

(1) Plasmogamy:- It involves the fusion of two protoplasts bringing two haploid nuclei class together in the same cell.

(2) karyogamy:- It involves the fusion of two haploid nuclei brought together during plasmogamy. This results in the formation of a diploid structure the zygote.

(3) Meiosis:- It follows nuclear fusion which takes place in all sexually reproducing fungi. It again reduces the number of chromosomes from diploid zygote nucleus to original haploid number in the daughter nuclei.

In fungi sexual reproduction is of following types:-

(a) Planoganetic Copulation:- Planoganetes are motile gametes. This involved the fusion of two naked gametes. The fusing gametes may be isogametes, anisogametes or heterogametes.

(b) Gametangial Contact:- In this case the gametes are transferred directly from one gametangium to the other. These gametes are undifferentiated protoplasts and are represented by nucleus. They never fuse.

(c) Ganetangial Copultion:- it involves the fusion of entire contents of two gametangia.

(d) Spermatization:- In some cases like ascomycetes and basidionycetes there is the formation of certain non motile male cells the spermatia. They are brought in contact with female. Gametangia, receptive hyphae or somatic hyphae to which they are attached. Partition wall dissolves and contents of spermatia pass into females organ.

(e) Somatogamy:- In most of the member of ascomycetes and basidiomycetes there are no sexual organs and the sexual act is a accompanied by fusion of two nuclei from somatic cells. This fusion results the formation of zygote, zygospore or oospore. They produce spores which in their turn develop into new mycellium.

Merits and Demerits of Fungi | economic importance of Fungi

 Fungi include many species which are of economic importance to man our lives are linked with Fungi. We are harmed and benefited by Fungi directly or indirectly. Some account for beneficial and harmful activities of Fungi is as under:

Useful activities of Fungi:

(1) Destruction of organic waste: Saprophytic Fungi decompose plant and animal remains by acting as natural scavengers. Carbon dioxide released in the process is used by green plants. By some workers saprophytic Fungi have been designated as vegetative vultures.

(2) In Industry:

(A)       Many fungi are used in the commercial preparation of many organic acids and some vitamin preparation. Aspergillus miger, A. glaucus, A. clavatus, citronyces citricus have been recommended for preparation citric acid. Many fungi also prepare gluconic acid lactic acid.

Aspergillus and Fusaruim are source riboflavin, a constituent of vitamin B. Yeasts are also rich in vitamin B.

(B)       Recently Fungi have been founded to be the basis of entire alcoholic industry. The basis of alcoholic industry is production of ethyl alcohol by fermentation of sugar solutions by yeast. Yeasts are source of complex enzyme zymase which is responsible for the process of fermentation. Yeasts are used in making wines, bear and ciders.

(C)       Certain yeasts Saccharamyces cerevisiaes form important basis of baking industries.

(D)       Some fungi such as species of Penicillium are used in preparation of certain cheese.

(3) As food: Many fungi like mushroom (Agaricus), Puffballs (Lycoperdon), Morels (Morchella) are edible. They are important as protein sources. They are regarded as delicacies of table.

Large scale production of yeast is used in conversion of carbohydrates and in organic nitrogen salts in to edible and nutritional forms. Yeast food supplies a number of vitamins like thiamine, riboflavin, micotomic acid, Panthothenic acid, biotin etc. Yeast food is there fore supplement of human food requirements.

(4)        In Medicines or Medicinal value: Recently many fungi have been founded to be responsible for producing certain antibiotic drugs which inhibit the growth of pathogenic micro-organisms. Some medicines formed from Fungi are Penicillin to kill bacteria that cause Pnemonia streptomycin. Auroemoycin, chloromycetin and Ephedrine from yeast.

(5)        In plastic manufacture: Certain Fungi like odium lactis is widely used in plastic industry.

(6)        Control and insect pest: Many Fungi like Ascherronia deyroides, Isaria ferinosa, Empusa sepulchralis help in controlling the infection of insect pests of the plants.

(7)        Phytohormone or Auxins: Many growth promoting substances like Gibberellins are synthesized from the fungi like Fusarium maniforma and Dematium pullulans.

(8)        Nutrition of plant: Many members of Phycomycetes, Ascomycetes, Basidiomycetes and fungi imerfecii are involved in the formation of mycorrhizae which are of fundamental importance in nutrition of tree like Cycas, Zamia and Pinus.

Harmful activities:

Fungi cause diseases to human, animals and plants. They cause destruction to clothes, paper, jute, leather, rubber, Paints, petroleum products, good grains and other bakery products. Harmful effects are:

(1)        Many fungi cause very much loss to our timber trees by causing wood rot. Armillaria mellea, the honey mushroom causes red rot of apple and many forest trees. Many species of Polypores attack forest trees causing wood rot.

(2)        Some would fungi like Rhizopus, Mucor, Aspergillus spoil our food. Their spores are always in the air and settle down on exposed jams, pickles, jelly, bread and fruits and develop mycelia and make food articles unfit for human use.

(3)        Some parasitic fungi are causative agents of diseased of our cops, fruits and other economic plants. In them fungi like Puccimia and ustilago cause rusts and smuts. They are great enemies of crops and cause loss by reducing crop yield. The rusts reproduce yellow, orange or black pustules on the stem and leaves of cereal plants while smuts attack forests and produces a black powdery mass of smut spores in the place of seed and fruits. Damage caused to cereals (wheat, maize, oat and barley) by rust and smuts amounts to several hundred millions of rupees annually. Fungi diseases in plants are:

(i)         While rust of crucifers by crystopus cindidus.

(ii)        Powdery mildew by Erisiphae species.

(iii)       Fruit root of apple by Rhizopus arrhizus.

(iv)       Late blight of Potato by Phytopora infestans.

(v)        Red rot of sugar came by colletorichum falcatum.

(vi)       Some parasitic fungi cause diseases to animals.

Saprolegnia which occurs as saprophyte on dead fish or flies behave as facultative parasite producing serious diseases to crops and gold fishes.

(4)        Some fungi are also cause some important diseases in human beings. Asperigillus as A.miger, A.fiavus, A.fumigatus are common human pathogens. Disease caused in aspergilloses of lungs and ears. Some parasitic fungi live in mucous membrane of throad, bronchii and lungs. Few fungi cause skin discoloration. A well known skin disease rung worm or “Dead” is also a fungus disease.

Economic importance of Algae

Many algae are used by human beings for food, manufacture iodine in some other purposes from ancient times. Many researches are being done in phycology (study of algae) and many workers are trying to find out the food value of algae, their importance in industries and importance in agriculture. The importance of role played by algae in the world is be coming more appreciated each day because of the increased utilization that many of them are valuable to man. Value is as under.

(1) Algae as food: Large numbers of Algae are used as source of food by human beings. They are rich in carbohydrates, inorganic substances and vitamins. Vitamins A C D and E are main constituents of these plants. Parphyratenesa is very popular and eaten throughout Japan. Kambu is another product of algae. Laminarta is used in Japan as standard food. Spirogyra is chief source of food ulva (sea lettuce) is also used be man as food. Recently green algae chlorena has drawn attention of psychologists. Percentage of Protein in this algae is too much than other vegetable or egg. It contains vitamins A to D. Algae is used to decorate pastries, sandwiches, rice, fish, cakes and jelly cakes in Japan. Agar Agar is also used in preparation of ice-cream and jellies. Geliduim, Gracillaria algae are chief source of agar agar. Another algae Rhodomenia palmata is chewed like tobacco in Scotland. Hair vegetable is eaten in China and algae Nostoc commune is one of its constituents. Minute algae chlorella has also been found as food source for human and animal. Many algae are used as food for animals like sheep, goat and cattle in New Zealand.

(2) Algae in industry: Diatoms (an algae) prepare diatomaceous earth and is extensively used in sugar refineries and soap manufacture. It is also helpful in cement industry, in the manufacture of dynamite, rubber and blotting paper. It is also used in isolation of boilers, blast furnaces and at various other places where very high temperature (1000°C) is required.

Algin is extracted by boiling algae I washing soda solution and rollers of type writers are prepared from it. Japanese prepare artificial wool from sargassum. Agar-Agar obtained from algae like Geliduim is used I sizing of textiles. Algae chondrius and careragaenium which yields a mucilage is used in manufacture of left hats as stiffening agent. It has the properties of agar and therefore used as ingredient of cosmetics, shaving creams, shoe polishes and shampoos. Various red algae like lamineria yields Iodine. Several sea weeds also yield bromine, acetic acid, formic acid and acetone.

(3) Algae in Agriculture: Presence of mucilage in most of the members of Myxophyceae helps in development and better nourishment for nitrogen fixing bacteria. Some of them like Anebena, Nostoc etc are able to utilize and fix atmospheric nitrogen, thus increasing soil fertility. Some members of myxophyceae were able to fix 20 Lbs. of atmospheric nitrogen per acre in rice field.

(4) Medicinal Use of Algae: Green unicellular algae chlarella yield an antibiotic known as chlorellin. It is crystalline and stable at 120°C. With an average composition of carbon 77.3%, Hydrogen 16.6% and oxygen 10.99%. It has marked effect on gram positive and gram negative bacteria. Presence of chara and Nitella algae in a pond cause death of mosquito larvae thus helping in control of malaria to some extent.

(5) Algae in Biological research: Photosynthesis and metabolism are based on studies of unicellular algae such as chlorella. Certain algae like chlamydomonas are being used in genetical studies. Chlamydomonas was the first haploid organism on which successful hydridization was accomplished.

Certain algae like Aceta bularia, Valonia and Nitella show great success in studies on morphogenesis, nuclear function, nuclear cytoplasmic relationship and ionic exchange with the environment. 

From above discussion it is clear that algae are great importance for human being.

Modes of perennation in fresh water and subarial algae

Perennation includes methods employed by plant to pass through unfavourable period for vegetative growth. In perennation period normally all the activities of organism cases and to pass through these unfavourable periods the living organism  develops some stage in life cycle which is protected by thick persistent wall. Marine algae live in conditions where variations in external conditions of life are rare. The freshwater and sub aerial algae are however exposed to the dangers of desiccation and extremes of temperature. They develop certain devices which enable them to carry through the period of sever conditions into the next growing season. Protective devices constitute the means of permeation. Main methods of perennation is fresh water and sub aerial algae are (a) Akinetes (2) Aplanospores (3) Palmella Stage (4) Cysts (5) Bulbils and amylum stars (6) Oospore or Zygote.

(1) Akinetes:- These are formed during conditions of draught eg. In ulothric, cladophora, pithophora, oosgonium and nostor. Akinetes are produced ogengly in each cell by rounding off cytoplasmic contents of the cell. The thick wall of the spore fuses with the parent cell. Entherie filament dies leaving behind the akines. Thuge survive and develop into new plants with the return of normal conditions of life.

(2) Aplanospores:- In some algae like chlamydononas, vlotherix, coleochacte, oedogomium the plant cells form thick walled non motile aplanospores during unfavourable conditions. During their formation the cytoplasmic contents round off and develop thick walls. These are then liberated by dissociation of parent wall. After a period of rest at the approach of favourable conditions they develop into new plants.

(3) Palmella Stage:- Under advese conditions in some green algae such as chlamy domoras, the vegetative cell divide, to form new daughter cell. These increase in number by repeated cell division. All the cells remain clustered together inside mucilage envelop formed by gelatinisation of parent cell wall of the successive generations. This is the palmella stage. It is of short duration and represents milder method of perennation.

(4) Cysts:- During unfavourable conditions the plant body of certain algae like vaucheria becomes separate. Each segment germinates directly into a new plant on the approach of favourable conditions.

(5) Bulbils and Amylum Stars:- In chara the tuberous bulbils and amylum stars also serve as a method of perennation. The amylum stars contain a large amount of starch gramules. They germinate.

(6) Oospore or Zygote:- Formation of zygotes method of perennation in green algaye. The zygote which is formed as a result of sexual fusion are thick walled structure with plenty of food material. Zygote usually undergoes a period of rest tot tied over the unfavourable conditions and then germinate into new plants either directly or indirectly by forming zoospore.

Origin and Evolution of sex in Algae

Sexual reproduction is characterised by the fusion of two similar or dissimilar cells. This is a sign of relatively advanced stage in evolution. Sex is not an obvious in the lower plants (like algae) as it is in higher plants. But in any way the study of reproductive processes of various classes of Algae throws considerable light on the origin and evolution of sex in the branch of plants like Algae.

Origin of Sex: Most primitive algae the cyanophyceae (Myxophyceae) reproduce only the method of asexual and vegetative reproduction. Sexual reproduction is entirely absent in their case. In forms like Nostoc and oscillatoria, it takes place by means of hormogones in which the plant body breaks up into group of few cells. In class xanthophyceae, chrysophyceae, cryptophyceae and dinopphyceae, sexuality is rare and has not much evolved beyond the stage of isogamy.

In higher classes of algae reproduction takes place by vegetative, asexual and sexual methods. The commonest method of asexual reproduction is by means of Zoospores. The possibility of gametes from zoospores can evolved from the following description.

In genera like ulothrix, ordogonium, cladophora, zoospores were probably produced before the origin of sexual reproduction. In ulothrix three types of swarm spores are formed.

(i)         Quadriflagellate macro-zoospores: They are produced either singly or in small numbers from a single cell. These swarmers are capable of developing into normal plants.

(ii)        Macro-zoospores: They are either quadriflagellate or biflagellate and are produced in greater number from each cell than macro-zoospores. They give rise to vary weak plants which are smaller in size.

(iii)       Gametes: These are always biflagellate, smaller than the micro-zoospores due to more division in the protoplasts of the cell and hence are largest in number. They are unable to develop into any plant individually but if two of these come together they behave as gametes and fuse leading to the formation of a zygote which germinates into a normal plant.

Thus a gradual loss in vitality of swarmers can be traced, the end product (i.e. gametes) being largest in number but smallest in size and physically in capable of developing into usual plants. It is believed that there was a by chance fusion between these swarmers previously accustomed to reduce vegetatively and then the plants regularly took to the method of fusion or sexual reproduction. It may be concluded that the gametes are ordinary zoospores but reduced in size and unable to germinate without the stimules of sexual fusion. These biciliate gametes unite in pair (isogamy) forming a zygospore which forms a new plant. This proves the derivation of gametes from asexual swarmers.

Evolution of sex: In the evolution of sex, the trend is same in various classes of algae and the sex in all orders and genera has evolved from asexual bodies. Isogamy is the simplest mode of sexual reproduction where two morphological similar gametes fuse e.g.: chlamydomonas media and ulothrix. Isogamy gives rise to anisogamy where two morphologically dissimilar gametes fuse. Anisogamy may be advanced and primitive depending upon the difference in size and behaviour of the gametes e.g.: Pandoriva, Eudoriva, species of chlamydomonas.

Oogamy is most advanced type of sexuality where the two gametes are so dissimilar in shape, size, structure and function that one of them is known as oogonuim and other as antheridium e.g.: volvox, chlamydomonas and ordogobium. In chlorophyceae evolution of sex may be seen from isogam to oogamy when we study individual genera like chlamydomonas (C. media iroamous, C. brounii anisogamous, C. Coccifera oogamous) or order volvocales in which pandorina and endorina are anisogamous and volox is oogamous. In order ulotrichales family ulvaceae genus enteromarphs sexually ranges from isogamy to oogamy.

In Rhodophyceae isogamy and anisogamy are found. In Polysiphomia advanced oogamy is present in phacophycal ectocarpus shows isogamy and anisogamy. Anisogamy is also seen in cutariales. Fucus shows primitive type of oogornium. Sargassum shows advanced oogany because only one ovum is produced in oogonium after fertilization takes place.

It may concluded that in the evolution of sex in algae, the differentiation of gametes is associated with the differentiation of sex organ. It also shows that evolution of sex in algae has taken place from simplest type of the highest evolved type. 

Give an account of structure, reproduction and life history of Batrachospermum

It is fresh water red algae and belongs to class Rhodophyceae and normally lives in cool, well aerated clear and shady situations. Plant body is filamentous freely branched and gelatinous in texture. Plant is like a chain of delicate beads. Each bead consists of a whorl of densely branched laterals of limited growth. Main axis consists of single row of elongated cells placed one above the other. From main axis arise branches of unlimited growth. Also node cells give rise to filaments which grow downwards the next node covering the axis cells forming pseudo cortex. Each cell of filament consists of two layered cell wall outer of pectin and inner of cellulose, cells are unimucleaet and contain a large number of parietal chromatophores, each with a single pyrenoid. Growth takes place by an apical cell.

Reproduction: It takes place by sexual method.

Sexual reproduction:

It is advanced oogamous type. Plants may be monoecious and dioecious. Male reproductive organ is antheriduim and female reproductive organ is called carpogonuim.

The antheriduim (Spermatogonuim) is a spherical or oblong unicellular structures which arise at the distal ends of short laterals. They arise in large numbers. Each antheriduim produces a single non-motile spermatuim (male cell) the spermatia are unimucleate and probably have same specific gravity as that of surrounding water. Therefore they remain floating.

The capranguim or procarp consists of a swollen basal portion with an egg and a narrow elongated neck like trichogyne. The caprogonia arise terminally on the laterals. The constricted portion of caprogonuim separating the trichogyne from the basal swollen portion known as plug. The caprogonuim develops at the tip of the caprogonial branch which is usually 3 to 4 celled. The terminal cell of caprogonal branch enlarges and becomes flask shaped. The single nucleus of terminal cell forms the egg.

Fertilization: The spermatia on liberation are carried away by water to trichogyne at the point of contact of spermatia disorganize and the nucleus of the spermatium passes down into carpogonium and fuses with its nucleus. A wall develops at the base of corpogonium and zygote is formed .

Germination of zygote:

The nucleus of diploid zygote increases in size and divides meiotically into two daughter nuclei lying one above the other. One of the nucleus migrates into a lateral protrusion which develops to the side of carpogonium and is cut off by wall and form gonimoblast initial which develop gonimoblast filament.

Give illustrated account of life history of Ectocarpus

It is marine Algae remains attached to substratum by rhizoids. Some species may be parasitic or may occur on higher members like of order fucales. Plant body is branched and has brown filaments which are slender. Plant body is made up of two parts, a creeping portion which serves as holdfast and a number of branches which arise from it. Filaments are made up of single row of cells. Each cell is uninucleate small and rectangular and has many chromatophores containing brown pigment. Pyrenoids are also present in chromatophores. Growth of filament is intercalary. Plant is autotrophic in nutrition.

Reproduction: Ectocarpus reproduces by Asexual and Sexual method.

Asexual Reproduction: (A) This takes place by biflagellate zoospores produced in unicellular sporangia which are borne by diploid asexual plant. They start as simple globular cells filled with Protoplasm. Nucleus undergoes single reduction division followed by simple division.

Around each daughter nucleus protoplasm collects to form zoospore. Each zoospore is haploid structure bearing two flagella at its lateral side. On liberation zoospore swims and settles down and grows into haploid plant.

(B) Asexual Reproduction may also take place by formation of diploid biflagellate zoospore produced in plurilocular or Neutral sporangia. These are formed by terminal cells on the short lateral branches. Contents of these undergo repeated divisions followed by wall formation. As a result a number of cubical chambers of almost equal are formed. As there is no reduction division at any stage, so the zoospores form diploid plants on germination these zoospores form diploid plants.

(2) Sexual Reproduction: It takes place from isogamy to an isogamy. Fusing of motile gametes may be of equal size of they may be of unequal size.

They are produced inside the plurilocular sporangia borne on haploid thalli. Such sporangia which are borne of haploid thalli are known as gametangia. They produce gametes which are haploid in nature. Plants are usually monoecious. Isogametes or amisogametes on liberation from same or different plants unite and form a diploid zygote. This zygote gives rise to diploid plant which in turn may bear neutral or unilocular sporangia.

Alteration of Generation:

In Ectocarpus gametophytes and sporophytes are similar morphologically and both are capable of asexual reproduction by zoospores. Some plants are haplonts others diplonts and still others show a regular alternation of generation of gametophytes and sporophytes.

Reproduction:

It takes place by vegetative or sexual method.

1.         Vegetative Reproduction:

It takes place by fragmentation. During this process little adventitious hoots formed either as a resut of injury to the thallus or by activity of meristem, get separated from the parent plant and develop into new thatti.

2.         Sexual Reproduction:

It is ooganous type. Sex organs like antheridia and oogonia are borne within spherical or conical chambers called conceptables in the swollen tips of branches called receptacles. Species of Fucus may be homo or heterothallic. In homothallic species the antheridia and oogonia may develop in same conceptacle eg: Ficis furcantus or different conceptacles of the same plant eg: Ficis spiralis. Conceptacles open outside by small opening called ostoile.

The oogonuim (female reproductive organs) develops from the superficial cell of conceptacle. Cell divides into a basal and oogonial initial cell. The basal cell does not divide further and forms a stalk while oofonial initial cell is fertile and forms the oogonium. The nucleus of oogonium then undergoes successive divisions to form eight daughter nuclei. First two nuclear divisions constitute meiosis. Cytoplasm undergoes cleavage to form eight uni-nucleate parts. Each uni-nucleate daughter protoplast rounds on. Eight spherical eggs or oospores are thus formed. At maturity the oogonial wall thickens and becomes differentiated into three layers. They are inner most endochite, middle mesochite and outer most exochite. Exochite ruphures in water. Oognoia are still enclosed by inner two layers. These are set free as a package through the ostiole into surrounding water. Sea water causes mesochite to ruphire at its apex and unvaginate. This exposes endochite. Endochite also takes water and finally dissolves. The eggs float away as passive or non-motile.

The antheriduim (male reproduction organ) is produced on the ultimate tips of branched paraphysis of male conceptacles.

Each Antheriduim is small oval or spherical uni-nucleate cell borne on the tip of much branched paraphysis. Any cell of the wall functions as antheridial initial cell and it divides into a stalk cell and antheriduim proper cell. It enlarges to form a terminal antheriduim. The stalk cell usually produces a branch which pushes the antheriduim to one side and itself gives rise to a second. Antheriduim by the repetition of this process are formed branched prophysis. The nucleus of the antheridial cell divides into two, four, eight, sixteen, thirty two and sixty four nuclei. Each nucleus surrounded by bit of protoplasm is metamorphosed into biflagellate pyriform antherozoid or sperm. It has two laterally attached flagella and an eyespot. Outer wall of antheriduim ruptures and all the sperms enclosed by mucilaginous wall come out.

This inner layer of mucilage is softened and sperms are released. Sometimes whole f the antheriduim comes out of the conceptacle and releases the sperms.

Fertilization: It takes place inside the water. Several sperms surround an egg but only one fuses with egg and results in formation of zygote which diploid in nature.

Germination of Zygote: The zygote or oospore germinates to produce new Fucus Plant.

Give general features and classification of Phaeophyceae

General features of class phaeophyceae:

They are called brown algae, few live in freshwater and majority live in sea water. The body of plant varies from simple branched filaments to large leathery branched structures with highly differentiated thallus.

Unicellular, colonial or un-branched filamentous forms are not found in this class. There is interval differentiation of thallus into epidermis, cortex and medulla. The cell has usually two layered cell wall, primordial utricle, a nucleus and chromatophorus without pyrenoids.

Plants are brown in coloure due to presence of fucoxanthin in addition to chlorophyll. There are also present highly retractive colourless fucosan vesicles. Food reserve is found in the form of soluble complex carbohydrate like laminarin, mannitol and fat instead of starch.

Reproduction takes place by vegetative, asexual or sexual methods. Vegetative reproduction takes place by frognuentation.

Asexual reproduction takes place by pear-shaped zoospores or naked aplanospores except order fucales.

1.         Sexual reproduction takes place by isogamy and oogamy. Reproductive structures have two unequal laterally instead cilia. There is definite alternation of generation except order fucales.

Classification: It is based as structure, reproduction and life histories,

Kylin (1933), Fritsch (1935), Pappenfus (1947) and Smith (1955) worked on classification.

(i) Kylin in 1933 divided phaeophyceae into two subclasses (A) Iso-generate – includes five orders

(B) Heterogenerate – includes four orders.

2.         Pappenfus in 1947 included one more subclass cyclosporae which includes one order fucales.

3.         Smith in 1955 gavea detailed classification based on above said workers.

Describe briefly structure and life cycle of chara

Chara is aquatic attached to muddly or sandy bottom of the pools, lakes and slow flowing streams. Few species are marine. Plant body consists of an erect branched axis which may grow to 20-30 can. The axis has district nodes and internodes. From each node arise a whorl of laterals of limited growth called leaves. From the axis of some leaves branches of unlimited growth may arise. Each branch bears nodes and internodes. Plant is attached to substratum by colourless branched multi-cellular rhizoids which arise from lower nodes of axis.

Growth of axis in length takes place by means of single dome shaped apical cells. Each node has a plate of cells while inter-node consists of single elongated cells. Each cell has a cell wall made up of cellulose and deposit calcium carbonate. They contain a single nucleus, dense cytoplasm with many discoid chloroplasts.

Reproduction: In chara it takes place by vegetative and sexual method.

1. Vegetative reproduction: It takes place as under:

(i)         By amylum stars: Some of the cells of lower nodes form a mass of special type of cells which are star shaped and are called amylum starch as they contain amylum starch in their cells. They can give rise to new plant but their exact mode of development is not known.

(ii)        By bulbils: Some of the rhizoids or lower nodes may form bulbils which also give rise to new plants when detached.

(iii)       By Protonena formation: Some on the nodes protonena like branches are developed and they also form new plants.

2. Sexual Reproduction:

It takes place by male and female reproductive organs called globule (antheridium) and nucule (oogonuim). Mostly species are monoecious, a few may be heterothallic or dioecious.

Two structures are found just aposed at a node, nucule being above the globule.

Structure of Sex organs:

As we know the plant body of chara consists of main axis which bears nodes and internodes. From nodes arise branches of limited growth. This also possesses nodes and internodes. The sex organs are developed on the nodes of these branches. Structure of the globule or Antheriduim: Mature globule or antheriduim is circular in outline and red or orange in colour. Wall of globule consists of eight shield cells. Out wall of each shield cell is marked with many infolding giving the idea that wall of anteridium consists of more than eight cells but this in only apparent. From the centre of each shield cell there arise a rod like out-growth the manubrium which bears at its upper end primary capitytum cells which may form secondary and tertiary cells. Secondary capitulum cell bear, branched uniservate spermatigenous filaments which are divided into small segments by transverse septa. Each segment functions as a single antheriduim. Cytoplasmic contents of each segment give rise to single speematozooid or antherozoid. Each antherozooid is spirally coiled and biflagellate structure.

Development of Globule:

Globule like male reproductive organ arises in the axis of branches of limited growth from single superficial cell. This cell cuts off one or two discoid cell at its basal and then becomes spherical. The lower two cells form a pedicle while the upper cell enlarges in size and becomes hemispherical in shape. Upper spherical cell divides by two longitudinal and one transverse division to form octant (Scelled structure). This octant divides by two curved plates or shields) and form wall of globule. As the shield cells mature they develop red pigments and radial in growths. Middle eight cells elongate form a rod shaped manubrium which projects imvard from the centre of curved shield cells. Each of the inner eight cells becomes a primary capitulum borne at the tip of manubrium. Each primary capitulum buds off about 4 to 6 secondary capitulum cells which may further give rise of tertiary and quaternary ones. From each capitulum cell develop antheridial filament. Each antheridial filament consists of about 200 discoid cells the antheridia. Within each antheridium is produced single elongated spirally coiled and biflagellate antherozoid. When the globule or antheriduim is mature the shield cells fall apart and the antherozooids are liberated by gelatimisation of antheridial walls or through a pore formed in each antheridial cell.

Structure or Nucule or Oogonuim:

Nucule or Oogonium is short stalked body attached to the body of primary lateral or leaf or dwarf shoot or branch of limited growth just above the antheridium. A mature oogonium consists of a large oval or elliptical egg surrounded by a cover of five tubular cells which make two or more clockwise spiral turns around it. From the upper end of each of the tubular cells a cell is cut off forming the crown or corona of oogonium.

Development of Nucule:

Oogonuim or nucule, the female reproductive organ develops in the axil of the branches of limited growth on the ad axial side. It develops from single superficial ad axial cell. This cell under goes two divisions to form three cells. Lower neost cell elongates and forms pedicel, the middle cell gives rise to five peripheral cells and upper most act as oogoial mother cell. Each peripheral cell divides to form upper cell Corona cell and lower larger cell tube cell. Five Corona cells elongate many times become spirally coiled around oogonium. Nucule when mature, tube cells separate from one another below corona to form five small shits for entrance of antherozooids.

Fertilization: Tube cells of oogonium separate thus forms slit. Antherozoids enter by slits, only on succeeds in the formation of oospore or zygote.

Germination of Zygote: Zygote secretes a coloured wall around it and undergoes a period of rest within oogonium. It falls from plant sinks to bottom of pond where it germinates after few weeks.

Describe structure and Reproduction in Nostoc

It is blue green alga of filamentous form. Nostoc is present in ponds, ditches and other pools and also in soil. Few species lie in intercellular cavities of plants like duck weed and root of cycas and are called endophytic. Some lead symbiotic life with a fungus forming a lichen.

Each jelly like mass of Nostoc consists of many slender long and short inter woven filaments which look like chain of beads. Each filament is un-branched and consists of a row of rounded or oval cells like series of beads in a chain. There is often a gelatinous sheath convering each filament in which entangled masses of Nostoc filaments remain embedded. Each cell is differentiated into two regions called chromplasm and an inner colourless region called central body (as in oscillatoria).

The filament increases in length by cell division in one plane only. Some enlarged vegetative cells with thickened walls and transparent contents are seen to occur at frequent intervals and also at the ends are called heterocysts. A pore is present at each pole of the heterocysts maintaining cytoplasmic connection with the adjoining cells. There is one pore in the terminal heterocyst. At a later stage the pore is closed by a button like thickening of the wall called the polar molecule.

Reproduction:

Nostoc reproduces vegetatively by fragmentation of the filament and sometimes asexually by resting cells (Spores) called akinetes.

Fragmentation: The filament breaks up into at the junction of the heterocyst and the adjoining cell into a number of shore fragments called hormogonia. Each hormogonium grows in length by cell divisions in one plant only. The heterocyst may other wise be a food storage cell.

Akinetes: Here and there some vegetative cells of the filament may become enlarged and thick walled containing reserve food. These are resting cells (spores) called akinetes. Later they may germinate into Nostoc filaments.

Structure and reproduction of Oscillatoria

It is a dark blue green filamentous alga. It floats in ditches and shallow pools of water and on wet rocks and walls. Filaments of oscillatoria are entangled in masses which float on water. Each filament is slender, un-branched and cylindrical, consisting of a row of short cells. The individual cells are the oscialltoria plants and the filament is regarded as a colony. All the cells of the filament are alike except end cell which is usually convex and there is no differentiation into the base and the apex. Some empty cells occur in some of the filaments.

The protoplast of each cell is differentiated into two regions: a coloured peripheral zone the chromoplasm and an inner colourless zone the central body. Colour is due to the presence of chlorophyll and phycocyanin (a blue pigment), which diffuse through the chronmoplasm. There is no plastid. True nucleus is also absent. The central body however is regarded as an incipient nucleus with only some chromatin but without nuclear membrane and nucleolus. Cell division takes place in one direction only. Each filament remains enveloped in a thin mucilaginous sheath. Under the microscope a slow swaying or oscillating movement of the filaments with ends tossing from side to side may be distinctly seen. This is characteristic feature of oscillatoria. The filaments may sometimes exhibit a twisting or rotating motion.

Reproduction: In blue green algae reproduction takes place by vegetative method only. They do not bear any kind of ciliated body. Gametes and zoospores are altogether absent. In oscillatoria the filament breaks up into a number of fragments called hormogonia. Each hormogonium consists of one or more cells and grows into a filament by cell division in one direction. The hormogonium has a capacity for locomotion.

Structure and Reproduction in Spirogyra

It is a green free floating filamentous alga present in ponds, ditches and springs. Each spirogyra filament is un-branched and consists of single row of cylindrical cells. The walls are made up of cellulose and pectin. Pectin swells in water into a gelatinous sheath. Filament shows no difference in base and apex. Each cell has a lining layer of protoplasm, one or more spiral bands of chloroplasts with smooth, wavy or serrated margins and a distinct nucleus situated in the middle. The spiral chloroplasts are the characteristic feature of spirogyra. Each chloroplast has a number of nodular proplasmic bodies called pyrenoids around which minute starch grains are deposited. If the filament happens to break up into pieces, they grow up into new filaments by cell division.

Reproduction: It takes place by sexual method. It consists of fusion of two similar gametes i.e. isogametes and the process is called conjugation which takes place between the cells of two filaments. Sometimes conjugation takes place between two adjoining cells of the same filament.

(1) Scalari form Conjugation: When two filaments come to lie in contact in the parallel direction they form tubular outgrowths from their opposite or corresponding cells. These tubular outgrowths called conjugation tubules give the whole structure the approach of a ladder.

Their end or partition walls dissolve and an open conjugation tube is formed. The protoplasmic contents of each cell lose water, contract and become rounded off in the centre. Each contracted mass of protoplasm forms a gamete. All gametes are alike in appearance but gametes of filament (male) creep through the conjugation tubes into the corresponding cells of adjoining filament (female) and fuse with the gametes of that filament. Fusion of two gametes results in the formation of a thick walled zygospore which soon turns black zygospores are formed in a series in one filament (female) while the other filament (male) becomes empty except for a few vegetative cells here and there.

(2) Lateral conjugation: It takes place between the cells of same filament

(i) Chain type: Commonly an outgrowth or conjugation tube is formed on one side of partition wall and passage the gamete (male) of one cell passes into the gamete (female) of the neighbouring cell.

(ii) Direct Method: In some species male gamete pushes the partition wall and pierces it in the middle. By the opening thus formed the male gamete passes into neighbouring cell and fuses with the female gamete.

In lateral conjugation the gametes of alternate cells only move to the neighbouring cells and thus later on the zygote bearing cells are seen to alternate with the empty cells in the same filament. Sometimes conjugation does not take place, gametangium may become directly converted into a zygospore like body called a zygospore or partheuospore which germinates like the zygospore.

Tthe structure and reproduction in ulothrix

Body of ulothrix has un-branched filaments. Filaments contain short cylindrical cells joined end to end. Cells are as broad as long. The filament remains attached to substratum by modified based cell called hold fast. Upper cell or tip cell is sub spherical in outline. Each cell except hold fast cell has got an outer wall composed of cellulose plus pectic substances.

Within the cell wall is cytoplasmic layer in which nucleus is embedded. Chloroplast has two more pyrenods. Filament is autotrophic in nutrition and grows in length.

Reproduction: It takes place by vegetation, Asexual and Sexual method.

(1) Vegetative Reproduction: It takes place by chance but not by regular method of multiplication. In this case the filament breaks up into two or more parts and each part is capable of converting itself into a new filament.

(2) Asexual Reproduction:

(A) By zoospore formation: The cell of filament under favourable conditions produces the zoospores. The zoospores are produced by ordinary cells of the filament whose contents divide into 2, 4, 8 and 16 parts. Zoospores are (i) Macro zoospores which are slightly flattened and have four flagella and (ii) Micro zoospores which are ovoid and have four or two flagella. Each zoospore is uni nucleate and has a chloroplast in broader part of spore and the apical part consists protoplasm and flagella. After liberation the spores swim for some time and come to rest, attach themselves and grow out directly into new filament.

(B) By Aplanospores: Occasionally the development zoospores stop just before development of cilia. In such cases non motile thin walled aplanospores are produced instead of motile zoospores. These aplanospores may germinate inside the parent cell or may be liberated outside. They then develop into new filament.

(C) By Akinetes: Sometimes in unfavourable conditions cell of the filament forms a single rounded thick walled structure called akinete. Akinetes are double walled with exospore and endospore. On return of favourable conditions the exospore ruptures and it develops into new filament.

(D) Palmella stage: Sometimes the contents of cell divide and their walls become mucilaginous. These cells either directly form new filaments or they give rise to zoospores which form new filaments.

(3) Sexual Reproduction: It is oogamous. Sexual reproduction consists simply fusion of similar two gametes. In unfavourable conditions each cell of filament produces 16, 32 or 64 gametes by divisions on the same manner as zoospores are produced. Isogametes are avoid and biflagellate. Each has chloroplast and a single pyrenoid. Isogametes come out of parent cell in membranous vesicle. Very soon the vesicle disappears and gametes move freely in the water.

Gametes fuse in pairs interiorly and quadric-flagellate zygospores or zygotes are developed. The cilia of zygotes are withdrawn, it becomes round and thick wall is secreted around it. Zygote after a definite resting period increases in size and its nucleus divides by reduction division. Protoplast of zygote divides and re-divides and 4 to 16 aplonospores or zoospores formation takes place. Each one of them develops into new filament of ulothrix.

Structure and Life Cycle of Chlamydomonas

It is unicellular green algae found in standing water of ponds, pools and ditches. Each cell is biflagellate spherical in shape. Cell wall is thin anterior end of chlamydomonas is papillate. At anterior end at right angles of the flagella are two contractile vacuoles. They help in excretion and respiration of the plant. Towards this end on one lateral side is an eye spot or stigma which is reddish or brownish red in colour due to a pigment harmatochrone. This eye spot is sensitive to light. Each cell has a basin shaped or up shaped chloroplast on posterior regions. There is single pyrenoid towards the base of chloroplast. Starch is formed around the pyrenoid. Nucleus lies in the centre of cell.

In nutrition cells of chlamydomonas are autotrophic due to the presence of chloroplasts water and inorganic salts are absorbed over whole surface of the cell.

REPRODUCTION:

It takes place either by asexual or sexual method.

(1) Asexual reproduction

(i) by Zoospore formation: This type of reproduction occurs in favourable conditions. Active cells of organism comes to rest, the flagella re withdrawn, and the ell contents divide into four, eight or sixteen parts, which become zoospore. These daughter individuals develop their individual cell wall and flagella. The parent cell wall is lost and the new individuals attain independent existence. They grow and develop into new chlamydomonas.

(ii) Palmella stage: Under favourable conditions the pond becomes dry. Zoospores remain enclosed within the parent cell wall, it grows in size and divides and large number of zoospores without flagella may be found in clusters inside an envelope of mucilage. This aggregation of cells is called palmella stage. On approach of favourable condition cell change to motile condition.

(2) Sexual Reproduction:
It takes place by fusion of gametes and is isogamous. Inchlamydomonas sexual reproduction is variable from isogamy to anisogamy and oogamy. Some species are monoecious and others are diocious.
In clamydomonas media and C debaryana the sexual reproduction is isogamous. In this case contents of cell divide to form 2 to 64 biflagellate gametes (like zoospores). Gametes may be naked or may have a cell wall. These are identical in shape and size and are called isogametes. They unite in pairs from their anterior end and form quadric-flagellate zygospore. It then loses cilia and becomes rounded.
In chlamydomonas braumi sexual reproduction is of amisogamous type. One cell divides twice to form four big biflagellate gametes (female gametes) and other cells divide 3 to 4 times to form 8 or 16 small biflagellate gametes (male gametes). In this way gametes of different sizes are formed one big and one small gamete unit together which result in the formation of zygospore.

In chlamydomonas coccifera and Coogamum the sexual reproduction is of oogamous type. In male cell produces 16 or 32 small biflagellate male gamete and the female are produced singly non motile female gamete. Male and female gamete fuse together to form zygote.
Germination of Zygote: Zoospore of zygote is formed by fusion of gametes. When favourable conditions come, the zygote nucleus which is diploid (2n) divides by meiotic (reduction) division and then divides mitotically to form four zoospores which are biflagellate and contain haploid nucleus. They come out by the burting of zygote wall and develop into new individuals.

Structure of Thallus in Chlorophyceae

Plants of chloroplyceae show variations in vegetative structure from unicellular to multicellular forms. They are as under

(1) Motile Form:- In organisation of thallus these forms of algae are simplest. They are unicellular and remain motile. e.g. ehlamydomonas in green algae. This is spherical, unicellular, unimucleate and biflagellate structure with cup shaped chloroplast. The cells swim with the help of flagella.

Motile unicellular algae from celonies which move about in water with the help of flagella of peripheral cells. Each colony has definite number of cells arranged in specific manner e.g. volvox

(2) Palmelloid forms:- Palmella stage is a temporary phase in life history of many algae e.g. chlamydomonas but in certain member of chlorophyceae xanthophyceae, chrysophyceae, this state of existence becomes permanent. Plant body remains embedded in a common gelatinous matrix of reproduction e.g.: sphaerocystis.
FIG 1-C PAGE 16 ALGAE BY G.L. CHOPRA

(3) Cocoid forms: In members of order chlorococcales small non motile cells are held together to form non motile colonies with either a definite of indefinite number of cells. They are free floating colonies e.g. Pediastrum and Hydrodictyon.

(4) Filamentous forms: Some algae have thread like plant body. These threads are called filament. Filamentous forms are derived either from palmellate or unicellular motile forms. They contain filaments which are composed of several cells placed one above the other e.g. ulothrix, spirogyra and ordogonium. This is called branched filamentous habit. Sometimes filaments may be branched e.g. cladophora. This is known as branched filamentous habit.

(5) Heterotrichous forms: This type of thallus met within the chartophorals among green algae. It has prostrate creeping system and erect projecting system. Both systems are present in stigeocloneum while in others one of these systems is present and the other is less developed, reduced or completely suppressed e.g. Coleochaete, Draparnaldiopsis.

(6) Siphonaceous forms: Here unicellular body of plant is enlarged to from a non separate multinucleate sac. Protosiphon has un-separate, un-branched tubular thallus containing nuclei. In vaucheria thallus is branched and contains numerous nuclei. In caulerpa there is a complex development of coenocytic branches to form a thallus which may be as 10 cms in height with definite external forms.

(7) Complex forms: In chara plant body is highly developed. Plant remains attached to soil by rhizoids. These branches are of limited and unlimited growth, former bearing sex cells. Plant looks like Angiosperm. This indicates that there is evolution of vegetative form of unicellular to multi-cellular complex forms.

Life cycle of Vaucheria

Vaucheria is green freshwater alga found in ponds, ditches and wet soil. It is not free floating like spirogyra but is mostly attached to substratum by colourless rhizoids or holdfasts. It is thallus is single branched tubular filament. It contain many minute nuclei present in living layer of cytoplasm surrounding a large central vacuole. Such structure is called coenocyte. Septa appear in connection with reproductive organs.

Asexual reproduction:- It takes place by large solitary zoospore. During its development the apex of filament swells up, becomes club shaped and is separated from rest of filament by a septum. This club shaped body is called zoosporangium. Its protoplasmic contents become rounded off forming a single zoospore wall of zoosporangium, ruptures at the apex, and the zoospore escapes by terminal pore and begins to rotate. Zoospore is an oval body of large size. Central part of it is occupied by large vacuole and in surroundings zone of protoplasm.

There lie many small chloroplasts, giving the zoospore deep green colour. Whole surface of zoospore is covered with many short cilia arranged in pairs and under each pair lies a nucleus. Therefore zoospore is regarded as compound one. Zoospores escape and swim about freely in water by cilia and soon come to rest. Cilia area with drawn and cell wall is developed round them. After coming to rest zoospores germinate by produces colourless branches rhizoid and attaches the plant to the substratum.

Sexual Reproduction:- It takes place by the method of fertilization i.e. by sharply differentiated male and female organs. Male organs are antheridia and female organs oogamia and these are developed at scattered intervals as lateral outgrowths. In monoecious species of vaucheria antheridia and oogamia usually arise side by side on same filament, or on short lateral branches of it.

The outgrowth that forms oganium swells out, assumes a more or less rounded form and is cut off by basal septum. The apex of oogonium develops a beak either towards antheridium or away from it. The protoplasm of oogonium contains one nucleus and forms a single large female genete. i.e. the egg (ovum or oospore) which fills ooganium. Each antheridium arises as a short tubular branch by side of ooganium. The terminal portion of it is cut off by a septum then it becomes actual antheridium. As it matures it becomes much curved towards the oogonium. The protoplasm contains many chloroplasts and nuclei. Many male gametes or antherozoids are produced inside each antheridium. They are minute in size and are biciliated. Cilia point in opposite direction.

Fertilization: Self fertilization is common but in diochious species cross fertilization is present. Antheridium bursts at the apex and many antherozooids called around the beak which opens at about the same time.
Several antherozooids may enter the oogonium through the beak but only one of them fuses with the ovum, while the rest perish. After fertilization ovum becomes invested with a thick cell wall and is known as oospore. Oospore undergoes period of rest and germinates into a new vaucheria filament.

Illustrated account of life history of Volvox

It is fresh water colony forming free-swimming green alga found ponds and other pools of water during and after rains. Volovox has reached highest degree of colony formation. Each colony or coenobium consists of a few hundreds to several thousands cells arranged in peripheral layer to form a hollow sphere containing water or a dilute solution of gelatinous material. Each cell of colony has gelatinous sheath and cells are held together in a colony by sheaths secreted by individual cells. Cells are connected by delicate strands of cytoplasm. Individual colony freely swims about in water. Each volvox cell is like chlamydomonas. Each mature colony has two kinds of cells: numerous small vegetative cells and few large cells among them. Vegetative cell has two cilia protruding outwards and vibrating 2 to 5 contractile vacuoles, a central nucleus a cup shaped or plate like chloroplast with one pyrenoid and one eye spot. Vegetative cells do not divide. Large cells of colony are

Reproductive cells. These cells may behave as asexual in beginning of season and as sexual cells at close of the season.

ASEXUAL REPRODUCTION IN VOLVOX:

The enlarged cells called gonidia of mother colony after retracting their cilia and pushing back to the posterior side divide and re-divide in the longitudinal place and give rise to large number of cells in one plant, thus forming new young daughter colonies with mother colony. When cell division cease the cells turn round, develop cilia and form again hollow spheres. These are seen to float and slowly revolve within the much enlarged hollow portion of the mother colony. Soon by ruphire they come out of the membrane of mother colony or trough a pore in it and swim away as independent colonies.

Sexual Reproduction: In volvox sexual reproduction is oogamous. In monoecious species both types of gametes (male and female) are borne by same colony while in dioecious species these are borne by separate colonies.
The said gametes are borne by enlarged cells called gametangia (gamete bearing cells) which lie in posterior side of the colony. Some of these cells are antheridia or male reproductive organs, the protoplasm of which divides many times and produces a cluster of minute biciliate male gametes called antherizooids or sperms; while other cells are oogonia or female reproductive organs, the proplast of which forms a single large female gamete called egg or ovum. Egg is large passive and non motile while sperms are very minute, active and motile sperms may be in a plate like colony escaping from mother colony as a unit or these may be arranged to form a hollow spore. In former case the unit as it approaches an egg breaks up into individual sperms and in the latter case sperms are liberated singly. Mode of fertilization is oogamous. Sperms swim and enter by gelatinous sheath into organism lying in mother colony and one of the fuses with egg. Thus the fertilization is affected.

ZYGOTE:- After fertilization the zygote clothes itself with a thick spiny wall. It is set force from the mother colony only after the decay or disintegration of latter zygote sinks to bottom of pool of water and then after a period of rest is germinates with the approach of favourable reason. The protoplast of the zygote undergoes reduction division prior to germination. In some species the protoplast of the zygote divides and forms a new colony directly, whiten in others it forms a single bicliate zoospore which escapes by the rupture of the zygote wall and swims away. The free swimming zoospore then divides and forms new colony.

Describe methods of reproduction in ordogonuim

Algae are mostly unicellular. Algae bear mostly chlorophyll and they are autotrophic thalloid plants. They are present in a variety of habitats but majority of them are aquatic. Plant body does not show differentiation into various tissue systems. Reproduction is vegetative and asexual and sometimes sexual.
REPRODUCTION IN ORDOGONUIM:
It takes place by three methods i.e. vegetative, asexual and sexual.
1. Vegetative reproduction in ordogonium: It is simple type of reproduction in which the filament of ordogonuim breaks up into many small portions, each of which divides into new filaments.
2. Asexual reproduction in ordogonuim:
(i) By Zoospore: All cells of the filaments are capable of forming zoospore except basal and apical cells. Cytoplasm of zoospore forming cell

Zoosporangium contacts and a hyaline receptive spot is formed. Ring appears around the margin of hyaline area. Each zoosporangium forms a single zoospore liberated by transverse split near the apex of zoosporangium. Zoospore splits out of gelatinous membrane and swims freely in water. The zoospore is oval multi-ciliate structure with a single nucleus on germination the zoospore gives rise to new filament.
(ii) By Akinetes: During unfavourable condition a chain of 10 to 40 thick walled akinetes are formed. Each cell of the filament develops a thick walled akinete by rounding off cytoplasmic contents. They germinate directly into new filament.

(iii) Sexual reproduction: Sexual reproduction is oogamous type and is common in plants growing in standing water than following water. Sex organs are antheridia and oogonia. Plants may be monoecious or dioecious. It is of two kinds:
(a) Macraudrous Type: Antheridia are reproduced in filaments of normal size either separately or on the same filament which bears oogonia.
(b) Nanandeous Type: Here antheridia are not formed to the filaments of the normal size but on special dwarf male filaments called nanandria produced by special types of motile swarm spores called androspores.

Macrandrous Type:
Antheriduim: Antheridia are terminal or intercalary and are produced by division of antheridial mother cells. Any vegetative cell may function as antheridial mother cell. It divides into two unequal cells on upper and to form antheriduim lower sister cell divides again and again and a chain of 2 to 40 antheridia is produced. Protoplasm of each antheriduim gets metamorphosed in a single antherizoid. Two antherizooids may also be produced which swim freely in water.
Oogonuim:
Oogonia develop by terminal or intercalary oogonial mother cell which divides transversely and the upper daughter cell develops into an oogonuim. Each of oogonuim possesses one or two caps at its upper end. Each oogonium is rounded or avoid in structure with a hyaline spot at upper end. It consists of a large spherical egg cell.
Nanandrous Type: Oogonia are formed as in mancrandrous type. Antheridia are formed on special dwarf filaments or mannandria and hence manandrous species are dioecious. These dwarf males or nanandria originate by germination of special type of swormers called androspores which are produced singly in flat cells androsporangia formed by repeated transverse divisions of ordinary vegetative cells. Androspores may be produced on same filament which bears oogonia or on a separate filament. Androspores get liberated like zoospores and settle down on oogonium or on a supporting cell.

Distinguish between Algae and Fungi. Mention economic importance of Algae and Fungi.

Algae
1. Algae are green Thallophytes bearing green colouring matter chlorophyll.
2. Algae are autotrophic plants i.e. they manuface their own food with the help of chlorophyll.
3. Body of Algae is formed of true Parenchymatous tissue.
4. Cell wall is formed of true cellulose.
5. Algae live in water or wet substrata.
6. Reserve Carbohydrate in Algae is starch.
Fungi

1. Fungi are non green Thallophytes with no chlorophyll.

2. Fungi are heterotophic. They get food from decaying animal or vegetative matter or from tissue of living plants of animals. 

3. In fungi body is formed of false tissue or bsendoparenchyma formed of threads called hyphae. 

4. Cell wall is formed of Fungus cellulose or Chitin mixed with cellulose. 

5. Fungi live as parasites on other plants or animals or saprophytes on decaying animals. 

6. Reserve Carbohydrate in Fungi is Glycogen.

In structure they both are unicellular, multi-cellular, filamentous and reproduction or thyloid is then may be vegetative by cell division or by detachment of a portion of mother plant or a sexually be fusion or by spores or sexually be gametes.

ECONOMIC IMPORTANCE OF ALGAE:

(1) Many of sea weeds are used as human food being rich in carbohydrates and vitamins. They form important food for fish and many other aquatic animals, some are used as cattle feed.

(2) Large brown algae called helps are an important source of iodine.

(3) In coastal regions many sea weeds are used as fertilizers being rich in potassium and other mineral matters.

(4) Some red algae are source of agar-agar, a gelatinous substance which used as a medium of culture for bacteria and fungi in the laboratory as a mixing material in textile industry, as a solidifying material in the preparation of puddings and jellies, as a base for show polish, shaving cream, cosmetic etc and as a dying and printing material for textile goods.

(5) It is also used in medicine, big deposits of diatoms in sea beds called diatomaceous earth have a number of industrial uses as metal polish, tooth powder, heat incubators in boilers and furnaces and filters in refining sugar.

(6) Many green algae are a source of food for fish and many aquatic animals. They also purify the water by absorbing CO2 and giving out O2. 

(7) Blue green algae contribute to the fertility of the soil. Some of them are known to fix fee nitrogen but some of them are a mixture to water reservoirs, sometimes polluting water, particularly during summer rains.

ECONOMIC IMPORTANCE OF FUNGI:

(1) Food poisoning due to the infection of poisonous fungi is not uncommon. Ergot poisoning (ergotism) now and then takes place in those countries (colds) where rye (a cereal) is grown for bread.

(2) Many fungi (Asporgillus and Penicilluim) spoil bread and other food stuff.

(3) Many fungi grow on leather and leather goods paper and books, linen and cotton clothes, rubber goods, wood and even valuable optical leuses, and cause considerable damage and decay them.

(4) Damage to food grains vegetables and fruits in storage often infected by moulds in warm humid climate results in a heavy loss.

(5) Many fungi often cause serious disease of crop plants of grown for food and industry.

(6) Many fungi have proved to be useful to mankind in many ways. Many soil Fungi like certain bacteria act on dead bodies of plants and animals decompose them and make the soil fertile.

(7) Yeasts are source of vitamins and enzymes. Proper ripening and flavouring of cheese depends on use of some species of Penicillin. 

(8) Some fleshy Fungi are widely used as food to human beings. Some wild animals like rabbits and squirrels feed upon a variety of Fungi.

What is Cyanophyta? Describe cell structure and economic importance of cyanophyta

Cyanophyta is division of Algae which includes class cyanophyceae or myxophyceae and the plants included in it are called blue green Algae because their pigment is bluish green. C-Phycocyanin. They are containing chlorophyll. They bear no well organised cell organelles. Pigments are present in chromoplasm. Nucleus is primitive type and takes nuclear membrane and nucleolus. They bear no flagella and they can move by gliding action. They are unicellular colonial in form cells are present in common gelatinous matrix. Filaments are unbranched and uniseriate or may sometimes show preudobranching. Their structure is prokaryotic. Cell wall is formed of micro fibrils held together in mucilage sheath. Orientation of fibres may vary in different species and may be reticulate as Nostoc.
Cell wall is differentiated into four layers. It is formed of mucopeptides, Carbohydrates, amino acids and fatly acids. Pain pigments are chlorophyll a, c Phycocyanin and c Phycocrythrin and they give blue green colour to algae.
Membrane bound plastids and absent. Pigments are found embedded within lamellae composed of two membranes joined at the ends. These algae show gliding jerky movements. Reserve food material is starch and protein. In Nostoc specialized structures called heterocyst are present. They may be terminal or inter calary in position as in Nostoc. Actual function of heterocyst is not known but are supposed to be centre of N2 – fixation. Reproduction takes place by vegetative and asexual methods. Vegetative reproduction takes place by cell division, fragmentation and hormogonia-formation. Asexual reproduction is by akinetes, endospores, exospores, heterospores and mannocytes e.g. Oscilaloria.

Plant body is filamcutons and unbranched. Filaments are called trichromes each of which has many cells places end to end. Each cell of the trichrome is rectangular. Cell wall has cellulose and pectin compounds. Below cell protoplast in present bearing perephral pigmented portion the chromoplasm and a central colourless region the central body or centroplasm. Chromoplasm contains pigments and reserve food material. There are no definite chromatophores, the pigments are irregularly distributed in it. The central body or Centroplasm or incipient nucleus is the nucleus without nuclear membrane.
ECONOMIC IMPORTANCE:
Mucilage is present which helps in the development and better nourishment for nitrogen fixing bacteria. Anebena and Nostoc are able to utilize and fix atoms pheric nitrogen and increase soil fertility. It has been seen that some members of Myxophyceae (Cyanophyceae) were able to fix 20 lbs of atmospheric nitrogen per acre in rice field. Rice increase was made from 15 to 20%.

What is Algae? Give various kinds of Reproduction in Algae

Algae are small microscopic plants and are mostly aquatic. Chlorophyll and other pigments are present in the body. Algae can manufacture food by normal process of photosynthesis and are called autotrophic. Cell wall is made up of cellulose. Starch is reserve food material. They grow in habitat where light is present. Usually asexual reproduction takes place and rarely sexual, also vegetative. Vegetative Reproduction: In this process portions of plant body are separated to give rise to new individuals without any change in the protoplast. Under favourable conditions it takes place by fragmentation in which whole plant body breaks up into small units which grow independently. In mynophyceae it takes place by hormogones formation. E.g. Plenrococcus. Asexual Reproduction: It takes place by:
 (1) By Zoospores: Zoospores are formed division of contents of parent cell. In filamentous forms like ulothrix zoospores are formed from older cells of the filament. Cytoplasm is divided to form zoospores which come out from mother cell wall. Zoospores are formed in favourable condition. Zoospores are motile and may be biflagellate or tetra flagellate or multi flagellate e.g. Vaucheria.
 (2) Palmella Stage: Sometimes zoospores do not come out of mother cell but remain surrounded by mucilaginous thread inside the mother cell. On division they form colony shaped structure of Pumella. On liberation they form new plants e.g. Chlanydomonas.
 (3) By Aplanospores: Aplanospores develop in unfavourable conditions. When motile phase of zoospores in eliminated the bodies are called Aplanospores. Each spore is surrounded by a wall. E.g. Ulothrix.
 (4) By Hipnospores: When alpanospores become thick walled and undergo a long resting period they are called hypnospores e.g. Sphaerella.
(5) A Kinetes: The protoplasm of single cell converts in a single akinete. Sometimes they are formed in chains. Each akinete may develop into a new plant e.g. ordogonuim, ulothrix. 
(6) Auto spores: Plants like Scenedesmus and some other chlrococales the resting spores develop all the structures of the parent cell in which they are formed and are similar to it except in size. These spores are called auto spores.
 (7) Cysts: In unfavourable condition the plant body of some algae like vaucheria become separate by transverse septa. Each segment forms many layered thick walled spore called cyst. During favourable conditions the cyst develops into new plant.
 (8) Endospores: The endospores are formed within the cells in blue green algae and Bacillariophyceae. Sexual Reproduction: It takes place by sex cells called gametes produced in cells called gametangia. Fusion may be as under:
 (1) In algae like chlanydononas, cladophore and ulothrix gametes may be identical i.e. gametes are similar and these gametes are called isogametes and sexual process is called isogamous reproduction.
 (2) In some algae like chlanydomonas brauni fusing gametes are different in size i.e. smaller active gametes and larger passive gametes. This sexual union is called anigogamous reproduction. In both above cases product of sexual union is called zygospore.
 (3) In some cases like ordogonuim and volvox young gametes are different in size. One of the gamete is small and motile while other is large and non motile. Former is called male gamete and other is female gamete or egg or oospore. This type of sexual reproduction is called ooganous and the product is called zygote or oospore. Zygospore or zygote develops into new plant on germination they may behave us under:
(i) Outer wall bursts and the contents surrounded by innes layer grow into new plant e.g. spirogyra.
(ii) Contents within the wall divide by meiosis to form a number of motile or non motile meisospores each of which on liberation develop into new plant e.g. Ulothrix.
(iii) Zygote divides mitotically to give rise to a small or a large diploid plant which produces the meisospores e.g. cladophora.