Prokaryotic and Eukaryotic Algae PDF

PROKARYOTIC ALGAE  DIVISION CYANOPHYTA (Blue-green Algae) These are a small group of primitive algae characterized by presence of a blue-green pigment, PHYCOCYANIN, in addition to chlorophyll (together giving a blue-green colour)  CYANOPHYTA Cont’d Some specie...

PROKARYOTIC ALGAE  DIVISION CYANOPHYTA (Blue-green Algae) These are a small group of primitive algae characterized by presence of a blue-green pigment, PHYCOCYANIN, in addition to chlorophyll (together giving a blue-green colour)  CYANOPHYTA Cont’d Some species are truly unicellular, while in others, the daughter cells after divisions adhere together to form a chain of cells (filament) or a flat or spherical colony A great majority of them are freshwater dwellers and are often found in almost every stagnant pool, wet ground or in the form of road slime after rains  CYANOPHYTA Cont’d The cell structure is a primitive type There is no definite nucleus or any plastid, and the protoplast is differentiated into: ✓ a peripheral coloured zone – the CHROMOPLASM, and ✓an inner colourless portion – the CENTRAL BODY  CYANOPHYTA Cont’d The cell wall is made of cellulose and pectic compounds Carbohydrate occurs in the form of glycogen, starch being altogether absent A gelatinous sheath is a common feature in most of them Some filamentous forms, particularly Oscillatoria, exhibit a slow, spontaneous movement  CYANOPHYTA Cont’d Blue-green algae never reproduce sexually, nor do they bear any kind of ciliated body The common types of vegetative reproduction are: ✓cell division in unicellular forms ✓breaking up of the colony in colonial forms  CYANOPHYTA Cont’d ✓fragmentation of the filament into short pieces called HORMOGONIA in filamentous forms In some filamentous forms (except Oscillatoria), a vegetative cell may act as a resting spore called AKINETE One or more enlarged vegetative cells with transparent contents and thickened walls may be present in such forms  CYANOPHYTA Cont’d ✓These are called HETEROCYSTS AKINETES are thick-walled cells formed after a period of active growth that survive in a dormant state when conditions are unfavorable for further growth They may be produced singly or in a chain  CYANOPHYTA Cont’d They are larger than vegetative cells and have thick walls and granular cytoplasm with an abundance of cyanophycin granules The cell wall is indistinct from that of the mother cell They may remain inactive for many years  At germination the protoplast is released by rupture of the wall or through a pore before growth commences  CYANOPHYTA Cont’d HETEROCYSTS are specialized cells for nitrogen fixation In the process, N2 from the air is converted to ammonium When dissolved nitrogen compounds are low in the surrounding water, some vegetative cells differentiate into heterocysts  CYANOPHYTA Cont’d During differentiation additional walls are added to the wall and pores through the wall connect heterocysts to other vegetative cells Heterocysts are usually larger than vegetative cells, have light yellow- green colour from loss of their (phyco)biliproteins, and lack storage granules  SOME MEMBERS OF THE CYANOPHYTA Gloeocapsa Oscillatoria Nostoc Anabaena Rivularia Lyngbya  MEMBERS OF THE CYANOPHYTA Cont’d Gloeocapsa: Always unicellular, but often, 2 to 4, or sometimes several daughter cells are held together in a colony by a mucilagenous sheath Oscillatoria: Consists of a slender, unbranched, cylindrical filament Each filament is made up of numerous short cells.  MEMBERS OF THE CYANOPHYTA Cont’d All the cells are alike except the end cell. This is usually convex and the filament is not differentiated into base and apex. When a sheath is present as in Lyngbya, the term TRICHOME refers to the series of cells, while the filament includes the sheath and cells.  MEMBERS OF THE CYANOPHYTA Cont’d Lyngbya: Is similar to Oscillatoria, but its filaments have a firm mucilaginous sheath that normally extends beyond the terminal cell Nostoc and Anabaena: Both are characterized by unbranched filamentous forms made of beaded cells and the presence of heterocysts  MEMBERS OF THE CYANOPHYTA Cont’d They differ in the following respects: ✓Nostoc filaments are twisted and flexuous, forming a tangled mass and have a thick (but not very firm) sheath ✓Anabaena filaments are straight or slightly curved, more rigid, often free and with a thin sheath  Nostoc and Anabaena Cont’d ✓Nostoc filaments often lie embedded in more or less firm gelatinous matrix, while Anabaena filaments are often free or sometimes in a thin gelatin ✓In Nostoc the heterocysts are intercalary as well as apical, while in Anabaena they are intercalary ✓Akinetes are more frequent and much more elongated in Anabaena than in Nostoc  Nostoc and Anabaena Cont’d ✓Nostoc is equally terrestrial and aquatic, while Anabaena is mostly aquatic Some species of Nostoc are symbiotic and live within the tissues of land plants (e.g. in the thallus of Anthoceros spp.),or are the algal partner in some lichens. EUKARYOTIC ALGAE  DIVISION CHLOROPHYTA (Green algae) They are characterized by the presence of chlorophyll located in definite plastids (chloroplasts) They are mostly freshwater algae, but some species are terrestrial They exhibit a variety of forms: ✓Unicellular or colonial - being motile or non-motile  CHLOROPHYTA Cont’d Multicellular - being thalloid or filamentous Coenocytic (colony of constant size) The protoplast is well organized, having a definite nucleus (usually one in each cell or several in a coenocyte), and one or more distinct chloroplasts  CHLOROPHYTA Cont’d The chloroplasts contain one or more pyrenoids (rounded protein bodies surrounded by a starchy envelope) The cell wall is made of cellulose and often has a layer of pectose around it The gelatinous sheath may or may not be present  CHLOROPHYTA Cont’d Most unicellular and colonial forms are provided with whip-like structures called FLAGELLA/CILIA – often 2, sometimes 4 or many – for motility of cells or colonies The flagella/cilia are of uniform length and always formed at the anterior end of the cell  CHLOROPHYTA Cont’d In higher forms of Chlorophyta the flagella/cilia are restricted to the reproductive bodies – zoospores and zoogametes Primitive forms have two or more contractile vacuoles and a small eyespot  REPRODUCTION Vegetative reproduction takes place by cell division or fragmentation Asexual reproduction takes place by spores of various types: ✓A motile, ciliate spore (zoospore)  REPRODUCTION Cont’d ✓A non-motile, non-ciliate spore with a distinct wall of its own but produces within a mother cell (APLANOSPORE) A vegetative cell acting as a spore, having no wall of its own – the wall of the mother cell acting as the wall of the spore (AKINETE)  REPRODUCTION Cont’d Sexual reproduction takes place by isogamy, anisogamy or oogamy depending on the species Whatever the mode of sexual reproduction, some species are:  REPRODUCTION Cont’d ✓HOMOTHALLIC (i.e. the pairing gametes come from the same parent), while others are ✓HETEROTHALLIC (i.e. the pairing gametes come from two separate parents  REPRODUCTION Cont’d In many green algae, it has been observed that a gamete grows PARTHENOGENECALLY (i.e. without fusion with another gamete) into a new plant The gamete thus behaves as a spore and is called a PARTHENOSPORE or AZYGOSPORE  REPRODUCTION Cont’d Sometimes, as in Spirogyra, the gamete has no cilia/flagella and is called APLANOGAMETE ORIGIN AND EVOLUTION OF SEXUALITY IN THE CHLOROPHYTA The vegetative method of reproduction is the most primitive method of multiplication of individual plants Asexual reproduction by zoospores appeared later in the lower Chlorophyta possibly as a means of rapid multiplication  ORIGIN AND EVOLUTION OF SEXUALITY Cont’d Sexual reproduction appeared later and still continued right up to the highest division of the plant kingdom ✓ evidently to achieve something that was not possible by the other methods  SEXUALITY IN THE CHLOROPHYTA Cont’d This something is protection, ✓for the thick walled zygote – the result of the sexual act – is better equipped to withstand environmental conditions before it starts a new life  SEXUALITY IN THE CHLOROPHYTA Cont’d Sexual reproduction has other advantages too: ✓When conditions are favourable for vegetative activity, neither spores nor gametes are produced ✓When conditions are less favourable, sexual cells or spores are produced  SEXUALITY IN THE CHLOROPHYTA Cont’d ✓As the plant approaches the end of its life or when conditions are very unfavourable, sexual cells or gametes are produced The mode of reproduction is thus, greatly influenced by the changing environment and age of the plant  SEXUALITY IN THE CHLOROPHYTA Cont’d The origin of sexuality in the Chlorophyta appeared as a modification of the older asexual method And is directly correlated with the origin of sexual cells or gametes from asexual cells or spores (zoospores)  SEXUALITY IN THE CHLOROPHYTA Cont’d Because of their small size (owing to repeated divisions) ✓The gametes have lost the power of functioning individually They have thus, developed some kind of mutual attraction and freely come together in pairs and fuse This is the earliest indication of sexuality  SEXUALITY IN THE CHLOROPHYTA Cont’d It may then be rightly said that gametes are derived from spores (zoospores) It is also seen that spores and gametes are similar in several members of the Chlorophyta ✓eg. in Chlamydomonas, Ulothrix, and Oedogonium, except that the gametes are smaller and more numerous SEXUALITY IN THE CHLOROPHYTA Cont’d Once sexuality appeared, it established itself and its evolution through isogamy to anisogamy to oogamy, based on the differentiation of sexual cells and sexual organs, proceeds towards a high degree of complexity, possibly towards a state of perfection through successive stages  SEXUALITY IN THE CHLOROPHYTA Cont’d In the simple and primitive forms of Chlorophyta, there is fusion of two gametes (zoogametes) similar in shape and size This is called ISOGAMY as found in Chlamydomonas, Ulothrix, etc. The next stage in the evolution of sexuality is ANISOGAMY, as found in Pandorina, certain species of Chlamydomonas, etc. SEXUALITY IN THE CHLOROPHYTA Cont’d Here, a slight difference is noticed in the size of the gametes or in their behaviour: the first indication of differentiation into male and female A complete differentiation of gametes and gametangia into male and female is found in the advanced forms of the Chlorophyta  SEXUALITY IN THE CHLOROPHYTA Cont’d The union of such differentiated gametes is called OOGAMY, as found in Oedogonium, Vaucheria, etc. In all the Chlorophyta, however, the gametangia are single-celled  EXAMPLES OF MEMBERS OF THE CHLOROPHYTA Chlamydomonas Zygnema Pandorina Oedogonium Eudorina Vaucheria Ulothrix Caulerpa Chaetophora Chara Protococcus Spirogyra  DIVISION EUGLENOPHYTA (Euglenoids) Euglena is a most simple, unicellular organism The evolution of the higher forms of plants possibly started from it It grows in large numbers in polluted water containing organic substances and colours it green  EUGLENOPHYTA Cont’d It is a single-celled, naked, free- swimming organism It has a single flagellum, i.e. a long, slender, whip-like projection, which vibrates and helps the plant to swim It can also crawl by changing its shape  EUGLENOPHYTA Cont’d The protoplast contains a central nucleus, several green plastids, a contractile vacuole and an eyespot near the blunt end  DIVISION PHAEOPHYTA (Brown Algae) These are a group of seaweeds with a variety of peculiar forms and sizes They are widely distributed between tidal levels along sea coasts predominantly of temperate seas They are attached to rocks or some other substrata  PHAEOPHYTA Cont’d In colder seas they seldom go beyond a depth of 20m While in warmer seas, a few species may grow up to a maximum depth of 90m Some also grow as epiphytes or endophytes on/in other algae A few are free-floating Their colour ranges from brown to olive-green  PHAEOPHYTA Cont’d ✓Due to the presence in the chloroplast of a brown pigment FUCOXANTHIN, which masks the chlorophyll There are no pyrenoids The reserve food may be ✓A kind of sugar (and not starch) ✓Or, more commonly, a complex carbohydrate called LAMINARIN  PHAEOPHYTA Cont’d Some like Ectocarpus are short filaments While others, like Fucus and Sargassum, are usually a few cm to 1m in length Others are massive seaweeds, called GIANT KELPS (Laminaria: 2-9m, Necrocystis: 45m, and Macrocystis: 60-90m)  PHAEOPHYTA Cont’d They grow at or below the low tide level, extending far into the sea to a depth of about 90m Small kelps are only about a meter long Unicellular brown algae are not known to exist  PHAEOPHYTA Cont’d The body of the kelp is differentiated into ✓A basal root-like, branched HOLDFAST ✓A long or short ‘stem’ called STIPE ✓And one or more leaf-like blades called FRONDS, which have air bladders to facilitate floating  PHAEOPHYTA Cont’d Some species have fronds of massive size The Phyaeophyta (except Fucus and Sargassum) show a regular alternation of generation  PHAEOPHYTA Cont’d With different degrees of development of the sporophyte and the gametophyte The sporophyte and the gametophyte can be ✓ Similar (ISOMORPHIC, as in Ectocarpus) ✓Or dissimilar (HETEROMORPHIC, as in Laminaria) in external appearance  PHAEOPHYTA Cont’d And their motile cells (zoospores and gametes or sperms) are ✓Laterally biciliate ✓The two cilia being of unequal lengths ✓ In contrast with the apically ciliate cells of most algae  REPRODUCTION Motile reproductive bodies (zoospores and gametes or sperms) are universally present throughout the Phaeophyta Several species reproduce vegetatively by fragmentation of the thallus  REPRODUCTION Cont’d Most of them reproduce asexually, through zoospores or aplanospores (except Fucus and Sargassum) and sexually by isogamy, anisogamy or oogamy The zygote germinates without any period of rest. EXAMPLES Ectocarpus, Laminaria, Fucus, Sargassum  DIVISION RHODOPHYTA (Red Algae) The Rhodophyta form a big group of highly specialized marine algae They are very widely distributed in both temperate and tropical seas, particularly in the latter  RHODOPHYTA Cont’d Many species are found between the high tide level and the low tide level along coasts; a good number of species grow at depths of 60- 90m, a few at much greater depths, up to 180m They are mostly attached to rocks  RHODOPHYTA Cont’d There are, however, some epiphytic and parasitic varieties which grow on other algae Although mostly marine, about 50 species have been found to occur in fresh water Red algae are characteristically red or purplish in colour due to the presence of a red pigment called PHYCOERYTHRIN which often masks the presence of chlorophyll  RHODOPHYTA Cont’d Many red algae contain a small amount PHYCOCYANIN, the blue pigment of the Cyanophyta Fresh water species are often green in colour Red algae have a variety of forms – filamentous, ribbon-shaped, distinctly leaf-like and marked with veins, etc  RHODOPHYTA Cont’d They are mostly a few to about 25cm in length, while a few are as long as 1 to 1.3m Deep-water ones are much longer Gelatinous material is abundant in the red algae, either occurring within the thallus or forming a sheath in the filamentous forms  RHODOPHYTA Cont’d Some red algae are heavily incrusted with lime The cells may be uninucleate or multinucleate with one or more plastids, which may be or without pyrenoids  RHODOPHYTA Cont’d A sugar or, more commonly, a special kind of starch called FLORIDEAN STARCH accumulates in the cells as a result of photosynthesis There is a total absence of motile ciliate cells; zoospores are altogether absent and gametes are never ciliate  RHODOPHYTA Cont’d Members of the Rhodophyta are either haploid or they show a regular alternation of similar haploid and diploid stages, as in Polysiphonia EXAMPLES Polysiphonia, Batrachospermum  DIVISION BACILLARIOPHYTA (DIATOMS) These are commonly called DIATOMS and consist of mostly one-celled algae They are of infinite variety of forms and often of exquisite beauty The single cells may occasionally form filaments and colonies  BACILLARIOPHYTA Cont’d They are universally distributed in fresh water, as well as in salt water and also in wet ground  BACILLARIOPHYTA Cont’d In some parts of the ocean they occur in vast assemblage as floating PLANKTON They often occur in huge numbers in a small space Most diatoms are free-floating, but some are attached by a gelatinous stalk  BACILLARIOPHYTA Cont’d The cells of diatoms have walls composed of silica Each cell wall is in two overlapping halves which are arranged exactly like the two halves of a Petri dish  BACILLARIOPHYTA Cont’d The half which overlaps the other, like the lid of a Petri dish, is the EPITHECA The other half is the HYPOTHECA Fossil diatoms have formed huge deposits of SILICEOUS or DIATOMACEOUS EARTH, often of considerable depth, in various parts of the world