Write short notes on the following:

By amylum stars or starch stars formation: In this method some of the cells of the 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 a new plant by their exact mode of development etc. is unknown.

By bulbils: In this method some of the rhizoids or lower nodes may form bulbils which also give new plants when detached.

By protonema formation: In this method sometimes on the nodes. protonema like branches are developed and they also form new plants.

By Globule: Globule, the male reproductive organ, arises in the axis of the branches of limited growth, from the single superficial cell. This cell cuts off one or two discoid cells 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. The upper spherical cell divides by two longitudinal and one transverse division to form octant (8 celled structure). This octant divides by two successive curved plates or shields and constitutes the wall of globule. As the shield cells mature, they develop red pigments and radial in growth. The mature, shield cells expand laterally and thus a cavity is formed inside the globule.

When the globule or antheridium is matured, the shield cells fall apart and the antherozoids are liberated by the gelatinisation of antheridial walls or through a pore formed in each antheridial cell.

By Nucule: The oogonium or nucule, the female reproductive organ, develops in the axil of the branches of limited growth on the adaxial side. It develops from a single superficial adaxial cell. This cell undergoes two successive divisions thus forming three cells. The lower most cell elongates and upper pedicle and the middle cell give rise to five peripheral cells and upper, most act as an oogonial mother cell. Each of the peripheral cell divides transversely, forming an upper smaller cell, corona cell and the lower larger cell-tube. The five corona cells elongate little and mature into the corona. The five tube cells elongate many times and becomes spirally coiled around the oogonium. The terminal oogonial mother cell elongated vertically and divides transversely to form a short stalk cell and an elongated oval shaped oogonium containing a single uninucleated egg.

The nucule when mature, the tube cells separate from one another just below corona to form five small slits for the entrance of the antherozoids.

Algae is used by human beings for manufacture of Iodine, food and in some other purposes from ancient times. The importance of the role played

by algae is becoming more appreciated each day because many of them are extremely valuable to man.

The following discussion gives rise to value of algae for human being.

(a) Algae as food: The species of Algae are used as a food by human beings e.g. used as carbohydrates, inorganic substances, vitamins, A CD and E etc. At present a green algae chlorella has drawn the attention of physiologists. The percentage of protein in this algae is too much or even more than any other vegetable or egg. The physiologists in Japan, China, America are busy in finding out its value. This is also used to sandwiches, fish, rice, pastries, jelly cakes in Japan etc.

The Rhodymenia palmata type algae is chewed like tobacco in Scotland. The preparation of ice cream in America, from algae Macrocystis. We obtain colloidal gel which is used in many ways. The different types of aquatic algae serve as a main source of food of aquatic animals specially fishes which constitute a very important food for human beings.

(b) Algae in industry: This is used in soap manufacture, in Sugar refineries, in cement industry, in the manufacture of dynamite rubber and blotting paper, in insulation of ilers, in various other places where a very high temperature (1000°c) is required etc. Various red algae like laminaria yield Iodine, Several sea weeds also yield bromine, acetone, formic acid and acetic acid. From algae Agar-agar obtained like Gelidium, which is used in the sizing of textiles.

(c) Algae in Agriculture or in Nitrogen Fixation: The most of the members of myxophyceae helps in the development and better nourishment for nitrogen fixing bacteria. Some of them viz Anabaena, Nostoc etc are themselves able to utilise and fix atmospheric nitrogen, so increasing soil fertility. We see that some members of myxophyceae were able to fix 23 lbs of atmospheric nitrogen per acre in rice field.

(d) Algae in Biological research : Some algae viz chlamydomonas and some desmids are being used in genetic studies, chlamydomonas was the first haploid organisms of which successful hybridization was accomplished.

Certain algae viz Nitella, Valonia and Acetabularia show great success in studies on morphogenesis, nuclear function, nuclear cytoplasmic relationship and ionic exchange with their environment.

The knowledge of chemistry of photosynthesis and the other aspect of metabolism is based largely on studies of unicellular algae such as chlorella.

Chlorophylls: There are five types of chlorophylls. They are chlorophyll a, b, c, d and e. Chlorophyll a is present almost in all the classes of algae while chlorophyll b is found in Chlorophyceae and Euglenophyceae. Chlorophyll c occurs in Chrysophyceae, Bacillariophyceae and Phaeophyceae. Chlorophyll d is confined to Rhodophyceae and chlorophyll e is present in Xanthophyceae and the zoospores of Vaucheria. Chlorophyll a and b are closely related pigments and so commonly both the pigments are called simply as chlorophyll.

Xanthophylls: There are twenty Xanthophylls. They are yellow or brown pigments represented by a molecular formula C₄₀H₅₆O₂. They are closely related to the carotenes but contain oxygen in addition to carbon and hydrogen. They are soluble in chloroform and insoluble in water.

Carotenes: Carotenes are linear unsaturated hydrocarbons represented by a chemical formula C₄₀H₅₆. There are 5 carotenes. They are a-carotene, ß-carotene, y -carotene. e-carotene and lycopene. ß-carotene occurs in most algae, but it is absent in siphonales and to a lesser extent in Rhodophyceae. In characeae also ß-carotene is not found.

Phycobilins: These are the other group of pigments which are associated with protein. Phycobilins are of two varieties, Phycocyanin and Phycoerythrin. Phycocyanin is R and C types and Phycoerythrin is R, C, X and B types. Both Phycocyanin and phycoerythrin are chemically, closely related and water soluble pigments. Phycobilins commonly occur in red and blue-green algae. Rhodophyceae (Red algae) has R-type and Myxophyceae (blue-green) algae has C-type phycobilins. During the analysis Phycobilins can not be separated from protein. They are the complex mixture of protein and pigment (Phycobilin) and hence the name of phycobilin pigments have been changed to biliproteins.

There is no sexual reproduction but Nostoc reproduces asexually or vegetatively by the following methods:

(i) Hormogonia – During the favourable conditions the trichomes generally break from the place when heterocyst is united with a vegetative cell. After breaking up, the hormogonia form new filaments.

(ii) Heterocysts- The heterocysts are intercalary in origin and are generally isolated. The reproduction by heterocysts is not very common in this genus. In N. Commune, the heterocysts have been observed to give rise to new filament. The new filament is liberated by the breaking of the wall of heterocyst.

(iii) Akinetes or Arthrospore- These are formed when a colony is mature and conditions are unfavourable. They occur in between the two heterocysts. Each akinite is somewhat oval in outline having exospore and endospore. On the approach of favourable conditions they germinate by the repeated of thick exospore. The cytoplasmic contents by repeated divisions develop into a new filament.

In nannandrous species the antheridia are formed on special dwarf filaments or nannandria and hence the nannandrous species are dioecious. These dwarf males of nannandria originate by the germination of special type of swarmers called androspores which are produced singly in flat cells androsporangia formed by repeated transverse divisions or ordinary vegetative cells. The androspores may be produced on the same filament which bears oogonia or on a separate filament. In the former case, the androspores are termed gynandrospores and the species gynandrospores while in the latter case the androspores are called idioandrospores and the species indioandrosporus. The androspores resemble in shape and structure to zoospore, but they are somewhat smaller than zoospores and larger than antherozoids. The androspores get liberated like zoospores and after swarming and for some time the androspores settles down either on an oogonium or on a supporting cell. It then germinates to form a dwarf male filament on a nannandrium consisting of an elongated attaching rhizoidal cell and one or a few small discoid antheridia on the top of it. The formation of antherozoids and their liberation is an example of macrandrous type antheria.

Alternation of .generation is the type of life cycle that occurs in those plants and algae that have distinct haploid sexual and diploid asexual stages. In these groups, a multicellular haploid gametophyte with n chromosomes alternates with a multicellular diploid sporophyte with 2n chromosomes, made up of n pairs. A mature sporophyte produces haploid spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.

The haploid spores germinate and grow into a haploid gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes fuse to produce a diploid zygote, which develops into a diploid sporophyte. This cycle, from gametophyte to sporophyte, is the way in which all land plants and many algae undergo sexual reproduction.

In Fucus, reduction division (meiosis) occurs during the gamete formation in the antheridia and oogonia and therefore, the eggs and sperms become haploid. Such type of life-cycle is found in animals as well as in higher seed plants where the gametophytes are reduced to a few nuclei.

The plant body of chara consists of a main axis which is differentiable into nodes and internodes. From the nodes come out 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: The mature globule or antheridium is circular in outline and red or orange in colour. The wall of the globule consists of eight shield cell, the outer wall of each shield cell is marked with numerous infoldings giving the idea that wall of antheridium consists of more than eight cells but this is only apparent. From the centre of each shield cell there arises a rod like out growth, the manubrium which bears at its upper end a primary capitulum cells.

The primary capitulum may form secondary and tertiary cells. The secondary capitulum cell usually bears the branched, uniseriate spermatigenous filament which are divided into small segments by transverse septa. Each segment functions as a single antheridium. The cytoplasmic contents of each segment give rise to a single spermatozoid or antherozoid. Each antherozoid is spirally coiled and biflagellate structure.

Nucule or Oogonium: The nucule or oogonium is a short stalked body attached to the body of a 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, thus constituting the crown of corona of oogonium.

Antheridia and oogonia are micro- and macrosporangia. In the microsporangium four haploid cells are formed by meiosis which are potential microspores. Each potential microspore by mitosis produces gametophytes from which antherozoids are produced. Again the macrosporangia by meiosis produce four haploids, each one is a potential macrospore. Each macrospore by mitosis produces female gametophyte from which ovum is produced.

Anabaena reproduces entirely asexually by the following methods : –

(a) Hormogonia : Hormogonia formation is very common in Anabaena. In such case the trichome ruptures at places where heterocyst and the vegetative cells adjoin. In this way short segments of living cells are formed called the hormogonia.

The hormogonia slips out of the gelatinous matrix and establishes new colonies by division. The terminal cells of the hormogonia differentiate into heterocyst. The intercalary cells then divide in the plane parallel to the axis of the trichome forming a packet of cells. This is called aseriate stage

(b) Akinetes: Under certain conditions any cell or some vegetative cells of the trichome become enlarged and secretes a thick, highly resistant wall around it. They get filled with the reserved food materials. Such specially modified vegetative cells are called akinetes or resting spores. These are well adapted to survive the unfavourable conditions like water shortage and unsuitable temperature. The resting spores survive during the unfavourable conditions and with the return of the favourable conditions, they germinate into new plants.

The Cyanophyceae are characterized by the complete absence of sexual reproduction. No sexual organs and no motile reproductive bodies have been observed. Propagation takes place by simple division, by spores (akinetes, endospores, and exospores) or else by fragmentation (fission). The multiplication of unicellular and colonial forms is brought about mainly by simple cell division. In all the filamentous forms multiplication is largely affected by the formation of hormogonia. The hormogonia are the fragments of the filament delimited by the occasional death of cells at intervals along the length of the filament. In certain forms, the hormogonia are enveloped by thick sheath and thus are modified as organs of perennation, known as hormocysts or hormospores, which on germination grow out into new filaments.

Many of the filamentous forms produce heterocysts, which break up the filament into hormogonia. At times the heterocysts may behave as spores to germinate into new filaments. In some cyanophyceae, the akinetes germinate immediately after formation, while in others they remain dormant for long time, behaving as resting spores.

On germination the protoplast divides, producing germling. In a number of genera, particularly in certain unicellular members, small spores, known as endospores are formed endogenously within a cell. They arise by successive division of the protoplast along three planes. The endospores forming cell behaves as a sporangium.

The endospores are generally naked, but a thin wall is secreted after their liberation from the sporangium.

In some epiphytic forms the delicate cell wall ruptures apically exposing the protoplast from which spherical spores are abstracted successively from its tip, these are called exospores.

The protoplast is continuously active. The exospores may germinate when already attached to the parent protoplast giving rise to new individuals.

This simply involves the dissociation of different kinds of vegetative propagules from the plant body; each of these can develop a new plant.

(1) By Amylum Stars: The amylum star consists of several starch-filled cells arranged star-like. It develops at the basal node of the main axis.

(2) By Bulbils: These are tuber-like bodies developing on the rhizoids (e.g., C. aspera. In C. baltica the unilateral bulbil develops at the node of the main axis. Bulbils are the perennating bodies.

(3) By Amorphous Bulbils: These simply represent the clusters of several small cells, laden with reserve food. They may develop at the basal node of the axis (e.g., C. delicatula) or at the nodes of rhizoids (e.g., C. baltica and C. fragifera) as lateral outgrowths.

(4) By Secondary Protonema: It usually develops as a lateral appendage from the basal node of the primary protonema (i.e., juvenile plant). It is the filamentous photosynthetic structure divisible into nodes and internodes, and has filamentous rhizoids at its basal node. It is usually formed during the course of the germination of oospore.

The cell wall is stratified into three layers; of these, the outer and middle layers are of pectic compound while the inner one of cellulose. In some other species the middle layer alone is of pectose while the outer one of chitin.

The entire space of the cell is occupied by a peripheral shell of reticulate (= meshwork) chloroplast with several pyrenoids at its intersecting points. There is an elliptical nucleus at the mid-periphery of the cell, lying in the vicinity of vacuolated cytoplasm.

This is a big class which includes about 187 genera and 900 species. With a few exceptions, which inhabit fresh water, all members of brown algae are nearly marine. They may be lithophytes or epiphytes.

The plant body varies from simple branched filaments to large leathery branched structures with highly differentiated thallus. The unicellular, colonial or unbranched filamentous forms are not found in this class.

The larger kelps show an internal differentiation of the thallus into epidermis, cortex and medulla. The cells usually have two layered cell wall, primordial utricle, a nucleus and chromatophores without pyrenoids.

They are brown in colour due to the presence of fucoxanthin in addition to chlorophyll. There also the presence of highly refractive colourless fucosan vesicles.

The food reserve is round in the form of soluble complex carbohydrates like laminarin, mannitol and fat instead of starch.

The reproduction may takes place by means of fragmentation. The members of phaeophyceae reproduce asexually by pear-shaped zoospores or naked aplanospores, except the order fucales.

The sexual reproduction ranges from isogamous to oogamous type. The reproductive structures have two unequal laterally inserted cilia.

There is a definite alternation of generation except of order fucales.

In aquatic species normally the zoospores are produced as coenocytic, compound, multiflagellate, spherical or oval in shape. They are formed singly

in a zoosporangium. The zoospores are also called Synzoospores.

Formation of zoospores: Any branch of the filament becomes swollen at the apical end and functions as sporangium. The protoplast of the filament comes to the swollen end of filament, the vacuole disappears and the swollen end becomes club shaped. A transverse septum appears below the swollen end which separates this from the rest filament. The swollen end is the sporangium. The rearrangement of protoplast takes place in which all the nuclei come towards the periphery. The protoplast contracts slightly and all the nuclei produce two flagella towards outside. Thus the whole protoplast of the sporangium metamorphosed into a multi-flagellated zoospore.

When the zoospore gets maturity a pore appears at the apical portion of the sporangium. The zoospore escapes through this pore into water.

Germination of zoospore: The zoospore after liberation comes into water and swims for some time and then comes to rest at the bottom. Now the zoospore withdraws the flagella and secretes a cellulose wall around itself. At this stage the rearrangement of protoplast again takes place, as a result the nuclei comes to the centre and the chloroplast goes towards the periphery. The zoospore begins germination giving rise to two germ tubes. One of them forms rhizoid and the other (upper) forms the plant body.

A gonimoblast is a type of cell produced by red algae upon the fertilization of a zygotic nucleus, and involved in the formation of carpospores. The cells subsequently divide and ultimately serve as storage or generative cells. Storage cells contain starch and are multinucleate. Generative cells are – situated further from the auxiliary cell, are uninucleated, and form the terminal lobes in the ensuing carpospores. Gonimoblasts are connected by septal pores, usually blocked by septal plugs.

In spirogyra sexual reproduction occurs by conjugation, which is of two types-

(a) Scalariform conjugation : It is the most common type of conjugation in spirogyra. The two filaments function as male and female. Their cytoplasmic content is rounded up, leading to the formation of gametes. Via the conjugation tube, the male gamete is transferred to the female filament and fuses with the female gamete to form the zygote. The zygote becomes zygospore by developing a thick wall. The male filament is empty and the female filament carries the zygospore.

(b) Lateral Conjugation : This type of conjugation occurs within the same filament. In direct lateral conjugation, the content from one cell acting as male gamete moves into the adjacent cell acting as female gamete through a pore and the zygóspore is formed. In indirect lateral conjugation, the conjugation tube is formed between the adjacent cells and the male gamete content is transferred to the female gamete which is adjacent to the male gamete.

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