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CHAPTER -3, ALGAE: AN INTRODUCTION, General Characters, Range of Thallus, Organization, Reproduction, Classification,, Morphology and Life Cycle of some Genera &, Economic Importance

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INTRODUCTION (father of algology :F.E. Fritsch), The general term "algae" includes prokaryotic organisms — cyanobacteria, also, known as blue-green algae — as well as eukaryotic organisms (all other algal, species)., Algae are diverse group of relatively simple, chlorophyll containing, photoautotrophic and oxygen evolving aquatic thalloid (without differentiation into, true roots, stems, leaves or leaf like organs) organisms.,  The word algae has its origin from Latin, where alga means seaweed.,  The term algae was first used by Carolous Linnaeus in 1753.,  Most of them are photo-autotrophic but few are mixotrophic and myzotrophic, ( sucking through special feeding structure),  Study of algae is known as phycology (GK. Phykos- seaweed; logos= discourse, or study) or algology.,  Professor M.O.P. Iyenger, (Mandayam Osuri Parthasarthy Iyengar) is regarded, as the father of Indian Algology of Phycology.,  He discovered the terrestrial alga Fritschiella tuberosa.

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ECOLOGY AND DISTRIBUTION, Algae are mostly aquatic but they are present almost every available ecological, habitat on this earth., They are thus ubiquitous in their distribution., On the basis of their habitat they are:, 1. Aquatic Algae, 2. Terrestrial Algae, 3. Parasitic algae, 4. Symbiotic Algae, 5. Algae with some special habitats, AQUATIC ALGAE: most of algae are aquatic found in fresh water ( lakes, ponds,, rivers, ditches, tanks, streams, etc.) or sea (marine environment)., Bottom dwelling organism are called benthophytes (benthic algae or benthos) or, may be present on the surface of water bodies are called Phytoplanktons.

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RANGE OF THALLUS ORGANIZATION, Algae exhibits variety in their thallus organization and can be divided into the following broad, categories, 1. Unicelllular Thallus, 2. Colonial thallus, 3. Siphonaceous thallus, 4. Filamentous thallus, 5. Parenchymatous thallus, UNICELLULAR FORMS, , The plant body is made up of single cell. Which may be motile or non motile., Unicellular form are absent in Charophyta and Phaeophyta), i)MOTILE FORMS : show presence of flagella or due to presence of periplastic, nature., a) FLAGELLATED MOTILE FORMS:, e.g. Chlamydomonas, Phacotus, Chlorochromonas.

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b) PERIPLASTIC FORMS: etc., They have soft cell wall and possesses fine, protoplasmic projections known as rhizopodia, which, helps in amoeboid movement e.g. Rhizochloris,, Chrysamoeba, ii), , NON-MOTILE FORMS: Lack flagella,e.g. Diatoms,, Chlorella, Chlorococcum, Porphyridium and BGA (, Gloeocapsa, Anacystis, Spirullina )., 2. COLONIAL THALLUS: In this form daughter cells, which arise as a result of cell division, remain loosely, held together in common gelatinous mass. These, forms are of two types, i) COENOBIAL FORMS: colonial form with definite, number of cells arranged in definite manner., Coenobium are of two types

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a) MOTILE: They have flagella on their body, and are able to move e.g. Volvox, Eudorina,, Pandorina etc., , a) NON-MOTILE: They lack flagella e.g., Hydrodictyon, Pediastrum, Scenedemus, etc.

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II) CELL AGGREGATION: The daughter cells are not, aggregated in a definite manner in the colony thus the, colonies are not of constant size and shape. They are of, following types, a) PALMELLOID FORMS: Cells remain irregularly, arranged in a common gelatinous matrix. They, function as independent entities., These forms may be temporary (Chlamydomonas) or, permanent (Tetraspora) other e.g. Asterococcus,, Aphanocapsa., b) RHIZOPODIAL FORMS: In these colonial forms, cells, are aggregated with each other through rhizopdia, e.g. Chrysidiastrum., c) DENDROID FORMS: Cells are aggregated with each, other in a branching pattern through mucilagenous, strands arising from the base of each cell. Such, colonies look like a microscopic tree. E.g, Ecballocystis, Chrysodendron etc.

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4. FILAMENTOUS THALLUS: A thread like multi-cellular, thallus is known as filamentous thallus. These are of, following types:, i) SIMPLE UNBRANCHED THALLUS: The thallus is simple is, simple and unbranced and may be free floating as in, Spirogyra or may be attached to substratum with the, help of rhizodial cells, e.g. Ulothrix, Oedogonium,, Zygnema, Nostoc, Anabaena, Oscillatoria etc., ii) BRANCHED FILAMENTOUS THALLUS : Thallus give rise, to lateral outgrowth or branches which may be true or, false branches., a) TRUE BRANCHES: True branches arise as a result of, occasional cell division in a second plane e.g., Cladophora., b) FALSE BRANCHES: False branches arise in blue-green, algae e.g. Scytonema due to breakage and resumption, of growth by trichomes in mucilagenous sheath of, filaments, iii) HETEROTRICHOUS THALLUS: Highly evolved filamentous, habit where thallus is differentiated into creeping, prostrate and upright erect systems, e.g. Ectocapus,, Fritscheilla, Stigoclonium, Coleochaete.

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5. PARENCHYMATOUS THALLUS:, It is multicellular where cell, division take s place in two or, more planes., If cell division occur in one plane, only, flat foliaceous structure are, formed as in Ulva., If cell division takes place in, more than two plane, tubular (in, Codium, Scytosiphon etc.) or, complex, structure, (as, in, Sargassum)may be formed.

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REPRODUCTION, ALGAE, , IN

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REPRODUCTION, •Reproduction is the biological process by which new, individual organisms "offspring" are produced from, their "parents"., •Reproduction is a fundamental feature of all known, life; each individual organism exists as the result of, reproduction., •There are three forms of reproduction.

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TYPES OF REPRODUCTION, There are three common methods of reproduction found in algae., 1. VEGETATIVE REPRODUCTION, 2. ASEXUAL REPRODUCTION, 3. SEXUAL REPRODUCTION

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1. VEGETATIVE REPRODUCTION, • The vegetative reproduction in algae includes those methods of propagation, in which portion of the plant body become separated off to give rise to, individuals., • Process does not involve the meiosis, fusion of nuclei and production of, spores., • Very common mode of multiplication., • Vegetative reproduction take place by different methods.

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i) BY CELL DIVISION:, • The mother cells divide, and the daughter cells are, produced, which become, new plants., • It is sometime known as, Binary Fission., • This type of reproduction, is found in Diatoms ,, Euglena.

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ii) FRAGMENTATION:, The plant body breaks into, several parts or fragments, and each such fragment, develops into an individual.,  This type of vegetative, reproduction is commonly, met, within, filamentous, forms,, e.g.,, Ulothrix,, Spirogyra etc., The, fragmentation, of, colonies also takes place in, several blue green algae, e.g., Aphanothece, Nostoc etc.

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iii) BUDDING:, Bud like structure has been reported to, develop on the thalli of Protosiphon., iv) AMYLUM STARS: They are starch filled,, star shaped, cell aggregates present on the, lower node of member of Charophyceae., They germinate into new plant bodies., v) TUBERS: Tuber like structure develop on, the rhizoids of Cladophora and Chara., They accumulate food materials. When, detached, germinate into new plants.

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VI) ADVENTITIOUS BRANCHES, Adventitious Branches, are formed in some, large thalloid forms of, algae., These branch when, get detached from the, parent, thallus, develops into new, plant ., Adventitious branch, like protonema formed, on the internodes of, Chara ., E.g Dictyota , Fucus ., , Adventitious Branches

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vii) Hormogone formation:, • When the trichome's, break in small pieces of, two or more cells, such, pieces, are, called, ‘hormogones’, • In some Blue green algae, the fragments undergoes, a gliding movement which, are called ‘Hormogones’., • Each, hormogone, develops into a new, plant, e.g., Oscillatoria,, Nostoc etc.

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2. ASEXUAL REPRODUCTION, Asexual reproduction is a mode of reproduction by which offspring arise, from a single organism, and inherit the genes of that parent only., it is reproduction which almost never involves ploidy or reduction.,  The offspring will be exact genetic copies of the parent, except in the, specific case of automixis ., It involves the rejuvenation of the protoplasts., Asexual reproduction occur through following methods.

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i) BY ZOOSPORES:, These are motile and naked reproductive bodies, developed inside special structures, known as, zoosporangia., They possess two, four or many flagella and are able to, swim in water., Each zoosporangium may produce only one, (Oedogonium), in multiple of four (Ulothrix) or many, (Cladophora) zoospores inside them., Flagella may be present at he interior end (green algae), or on the lateral side (brown algae)., They are always formed in favourable conditions., The zoospores are always motile.

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2. APLANOSPORES :,  These are non motile spores produced inside sporangia.,  Mostly these are produced by terrestrial algae (e.g., Vaucheria) but also by Microspora and Ulothrix (aquatic, forms),  For their formation, protoplast of the cell rounds off and, develop its own wall to become aplanospore, also, considered as arrested zoospore.,  Sometimes aplanospores are similar to their parents, (Chlorella, Scenedesmus) in all aspect except size and are, known as autospore.,  Vaucheria produces minute size spore in large numbers, inside sporangium, known as microaplanospores., 3. HYPNOSPORES: These are thick walled, non-motile, aplanospores produced by some algae to tide over the, unfavourable conditions, e.g. Chlamydomonas nivalis,, Pediastrum, etc. on return of favourable conditions,, hypnospore germinate into new plant bodies., Chlamydomonas nivalis walls become red due to deposition, of haematochrome, responsible for Red Snow, phenomenon.

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4) AKINETES OR CYST:, • It is the types of reproduction very, common in the blue green as well, as green algae., • These akinetes are a type, vegetative cell which is thick, walled and will overcome the, unfavourable condition., • Sometimes they are formed in, chain., • In Protosiphon, akinetes are, formed multinucleate protoplast, to form coenocysts. They are, known as statospore in diatoms.

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5.MONOSPORES: These are haploid, naked, non-motile and uninucleate, spores produced singly inside the monosporangia during chantrantia stage, in member of class Rhodophyceae. They are liberated after the rupturing of, cell wall., 6.TETRASPORE: These are non-motile spores produced in groups of four,, inside specialized cells known as tetrasporangia., Tetraspores are sexual spores known as gonospores and meiospores, produced after meiotic division in diploid nucleus of tetrasporangium., found in Phaeophyceae and some member of Rhodophyceae, 7.NEUTRAL SPORES: prouduced by direct transformation of the protoplast, of a vegetative cell into a single spore, e.g. Ectocarpus., 8.CARPOSPORES: (Karpos= fruit +Sporo= seed) are non- motile spores, produced on short filament arising from carpogonium following fertilization., They are feature of red algae, e.g. Polysiphonia, Batrachospermum etc.

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3. SEXUAL REPRODUCTION

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Conditions for sexual reproduction:, (a) The sexual reproduction takes place, after considerable accumulation of food, material and the climax of vegetative, activity is over., (b) The bright light is the major factor for, the production of the gametes., (c) A suitable pH value is required., (d) The optimum temperature is, necessary.

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AUTOGAMY: Is the, fusion of two sister, gametes produced, inside the same, mother cell., In this process, only, karyogamy, takes, place., It, is, important, feature of diatoms.

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(i) Isogamy:, Isos=equal, alike, +gamos=marriage)is, the fusion of two morphologically and, physiologically similar gametes., Fusing gametes are known as, isogametes.,  The fusion of similar motile gametes is, found in many species.,  Usually the gametes taking part in, fusion come from two different, individuals or filaments, sometimes, these gametes come from two different, cells of the same filament.,  they cannot be classified as "male" or, "female." Instead, organisms undergoing, isogamy are said to have different, mating types, most commonly noted as, "+" and "-" strains, e.g. many spp. of, Chlamydomonas spp., Ulothix etc.

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(ii) HETEROGAMY:, The fusion of dissimilar gametes is called, heterogamy., There are two main types :, (a) Anisogamy:, (b) Physiological Anisogamy, a), ANISOGAMY:, (Gr., Aniso=unequal+gamos= marriage) is the, fusion of two morphologically and, physiologically dissimilar gametes., Fusion gametes are known as, anisogametes., Male gametes are smaller and more, active, while the female gametes are larger, and less active, e.g. Chlamydomonas, braunii, Pandorina etc.

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(b) PHYSIOLOGICAL ANISOGAMY: when, the fusing gametes are morphologically, similar, but, exhibit, different, physiological behaviour, the sexual, reproduction is known as phisiological, anisogamy., In this case one gamete is more, active and other is sluggish e.g., Chlamydomonas monoica, Spirogyra,, Ectocarpus., In E. siliculosus, the sluggish (female), gamete is surrounded by a large, number of more active (male) gametes, this type of fusion is known as clump, formation.

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iii), , Oogamy: (Gr. Oion= egg + gamos =, , marriage) is the fertilization of a large,, non-motile female gamete by small,, motile male gamete., It is most advanced and highly evolved, mode of sexual fusion and occur in, highly, evolved, algae,, e.g., Chlamydomonas coccifera, C. ooganum,, Volvox, Oedogonium, Chara, Fucus etc., In red algae Polysiphonia and, Batrachospermum where male gametes, are also non- motile, oogamy is more, specialized., Here male gametes are known as, spermatia and female as carpogonia.

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IV), CONJUGATION, OR, APLANOGAMY: is the fusion of, two similar, non-motile gametes, or cells which facilitate the, transfer of genetic material from, one cell to another., The fusing gametes are known as, aplanogametes., e.g. Spirogyra, Zygnema etc., V) PARASEXUALITY: The genetic, recombination, without, the, involvement, of, sexual, reproduction is known as, parasexuality, e.g. Anacytis, Anabaena and, Cylindrospermum.

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LIFE CYCLES IN ALGAE, The growth and development of algae passes through a number of distinct, morphological and cytological stages in definite orderly manner. This, sequence of orderly changes is called as life cycle or life history., It comprises the sequence of events from zygote of one generation to the, zygote of next generation., , There are five distinct types of life cycle as found in algae.

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HAPLONTIC LIFE CYCLE,  Most common type.,  Life cycle is diphasic.,  Prominent phase is haploid, gametophytic, phase., Sporophytic diploid phase is represented by zygote, only., Zygote is formed by the fusion of haploid gametes., Zygote immediately undergoes meiosis to form, haploid zoospores., Zoospore, on, germination, form, haploid, gametophytic generation, Gametophytic plant produce male and female, gametes by mitosis., This is the most simple and primitive type of life, cycles, found in Chlamydomonas, Ulothrix,, Spirogyra, oedogonium, Chara Bangia etc.

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DIPLONTIC LIFE CYCLE, This type of life cycle is the just reversal of, haplontic type of life cycle., Life cycle is diphasic, but the prominent phase is, sporophytic., , Haploid gametophytic phase is represented only, by gametes., Gametes are produced in the gametangia by, meiosis., Zygote donot undergo meiosis rather develop, into the sporophytic phase by mitosis., E.g. Sargassum, Fucus, Codium

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DIPLO-HAPLONTIC LIFE CYLCE:, Haploid and diploid phases are equally prominent, Gametophyte concerned with production of gametes,, which fuse to form diploid zygote, Zygote germinate to form diploid sporophytic plant, body, which is concerned with the production of haploid, spores., The haploid spores are known as meiospores and, geminate again to form gametophyte., In this type sporophytic (2n) phase alternates with, gametophytic phase equally., On the basis of morphological characters of, gametophytic and sporophytic plants, this life cycle is of, two types:, i)Isomorphic type: When both gametophytic and, sporophytic plant bodies are morphologically similar but, genetically different, this type of diplo-haplontic life, cycle is known as isomorphic or homologous life cylce,

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DIPHASIC HAPLO-BIONTIC LIFE CYCLE:, Two haploid gametophytic plant bodies, alternate with sporophytic phase of short, duration represented by zygote., Main plant body is free living gametophyte, concerned with production of gametes, Gamete fuses to form zygote, Zygote undergoes meiotic division and form, small parasitic haploid carposporophyte., Terminal cell of carposporophyte behave as, carposporangia, which produce haploid, carpospores, Carpospores germinates into haploid, gametophytic plant body, e.g. primitive red, algae such as Nemalion.

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Also, known, as, Diplodiplohaplontic., It is further of two type:, i)Isomorphic type: free living, independent generations, are, morphologically similar, e.g ., Polysiphonia., Heteromorphic :When two free, living, generations, are, morphologically dissimilar, also, known as heteromorphic or, heterologous.e.g, order, Nemalionales.

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CLASSIFICATION OF ALGAE

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CLASSIFICATION, • Fritsch’s Classification of Algae:, • F.E. Fritsch (1935, 1945) in his book “The Structure, and Reproduction of the Algae” proposed a system of, classification of algae. He divided it into 11 classes., His classification of algae is mainly based upon, characters of pigments, flagella and reserve food, material.