Phycology 2 PDF

INTRODUCTION Definition of Algae Algae are a diverse group of simple, plant-like organisms. Like plants, most algae use the energy of sunlight to make their own food, a process called photosynthesis. However, algae lack the roots, leaves, and other structures typical of true plants. Algae are the mo...

INTRODUCTION Definition of Algae Algae are a diverse group of simple, plant-like organisms. Like plants, most algae use the energy of sunlight to make their own food, a process called photosynthesis. However, algae lack the roots, leaves, and other structures typical of true plants. Algae are the most important photosynthesizing organisms on earth. They capture more of the sun's energy and produce more oxygen (a byproduct of photosynthesis) than all plants combined. Algae form the foundation of most aquatic food webs, which support an abundance of animals. Algae vary greatly in size and grow in many diverse habitats. Microscopic algae, called phytoplankton, float or swim in lakes and oceans. Phytoplanktons are so small that 1000 individuals could fit on the head of a pin. The largest forms of algae are seaweeds that stretch 100 m (300 ft) from the ocean bottom to the water's surface. Although most algae grow in fresh water or seawater, they also grow on soil, trees, and animals, and even under or inside porous rocks, such as sandstone and limestone. Algae tolerate a wide range of temperatures and can be found growing in hot springs, on snow banks, or deep within polar ice. The Study of Algae is called Phycology (Phycos = Algae, logos = Study of/Discourse of) and its history is quite old. Phycos is a Greek word which means seaweed and the references to algae are available in the early Chinese, Roman and Greek literatures. Roman named it Fucus, whereas Chinese called it Tsao. The ancient Hawanians used algae as food and called them Limu. The algae were used as manure on the north coast of France as early as the 12th century. General characteristics of algae 1. The algae are chlorophyll bearing organisms with a thallus-like plant body. 2. The thallus shows little differentiation of true tissues. 3. Even the complex thalli lack vascular tissue and epidermis with stomata. 1 4. The sex organs are one-celled, when multicellular, each cell is fertile and there is no jacket of sterile cells. 5. There is no embryo formation after gametic union. 6. Both the generations when represented in the life cycle are independent. There are no algae with a sporophyte parasitic on the gametophyte plant. 7. Excepting a few all the algae are aquatic. 8. Under favourbale conditions the gametophyte multiplies repeatedly by means of asexual spores called the mitospores. Occurrence of algae According to the habitat, the algae may be classified as follows : 1. Aquatic algae 2. Terrestrial algae 3. Algae of unusual habitats. 1. Aquatic algae: Majority of the algal genera are aquatic and found either completely submerged or free floating on the surface of water. Aquatic algae usually occur in ponds, pools, tanks, ditches, streams or in slow running rivers and are called fresh water forms. Marine algae are found in sea and macroscopic large thalli of brown algae are commonly known as "sea weeds". Fresh water algal forms like Chlamydomonas, Volvox, Hydrodictyon are found in stagnant waters, whereas Cladophora, Oedogonium, Ulothrix and few species of Vaucheria occur in slow running water bodies. Most of the members of Phaeophyceae and Rhodophyceae are found in sea either floating on the surface of sea water or attached with rocks or any other substratum. The free floating and free swimming microscopic algal forms together with other similar organisms constitute the Planktons of water bodies. Plankton forming algae may either be free floating from very beginning and are never attached (Euplanktons) e.g., Microsystis, Chlamydomonas, Scenedesmus and, Cosmarium or in the beginning may be attached but later on they get detached and become free floating (Tychoplanktons) e.g., Zygnema, Oedogonium, Cladophora, Cylindrospermum, Rivularia etc. 2 2. Soil algae: Many algal genera are found on or beneath the moist soil surface are called terrestrial algae. The algal forms occurring on the surface of soil e.g. few species of Vaucheria, Botrydium, Fritschiella and Oedocladium are called Sapophytes while algal genera having subterranean habit e.g., few species of Nostoc, Anabaena and Euglena are known as Cryptophytes. 3. Algae of unusual habitats: Many algae are found at various interesting places and according to their habitats may be of following types: 1) Halophytic algae. These algae are found in saline water containing high percentage of salts e.g., Dunaliella, and Chlamydomonas chrenbergii. 2) Lithophytic algae. Usually the members of Cyanophyceae grow on moist rocks, wet and other rocky surfaces. Blue green algae Rivularia and Gloreocapsa occur on exposed rocks, whereas Nostoc is found growing in damp shady habitats. Several marine belonging to Rhodophyceae and Phaeophyceae are lithophytic in habit and grow o submerged rocks or rocky surface e.g., Ectocarpus, Polysiphonia etc. 3) Epiphytic algae. Such algal forms which grow on the other aquatic plants are called Epiphytic algae. Green algae Chaetonema has been found growing on Tetraspora and Batrachospermum. Rivularia are observed to grow on Angiospermic plant. 4) Endophytic algae. Found inside the aquatic plants 5) Epizoic algae. Many algae grow on the shells of molluscs, turtles and fins of fishe are known was epizoic algae. Cladophora is found on snails and shells of bivalves. 6) Endozoic algae. Contrary to epizoic algal forms endozoic algae are found inside the aquatic animals e.g., Zoochlorella is found insiinside Hydra viridis while 3 Zooxanthe known to occur inside the fresh water sponges. 7) Aerophytes: Such algal forms as are adapted for aerial mode of life and occur on the trunks, moist walls, flower pots, rocks, and get their water and carbon dioxid requirements completed directly from atmosphere are called Aerophytes. Trentepohlia is found the bark of trees in moist and humid climatic conditions while Phermidium, Scytonema & Hapalosiphon have been observed to grow on bark of trees alongwith Bryophytes. 8) Cryophytes: These algae are found on the mountain peaks covered with snow and impart attractive colours to the mountains. Haematococcus nivalis gives red colour to Arctic and Alp regions while Chlamyodomonas yellowstonensis alongwith some species of Ankistrodesmus is responsible for the green colour of the snow of the mountain of European countries particularly in Arctic region. a) Those algae which are found on snow and not on ice e.g., some species of Raphidone and Chlamydomonas. b) Those algae which can grow only on ice and result in "ice bloom" e.g., Ancyclone, Mesotaenium. c) Those algae which can grow on snow and ice both e.g., and Cylmdrocys d) Those algae which are not true cryophytes and have their temporary growth on ice snow e.g., Phormidium and Gloeocapsa. 9) Thermophytes: The algal genera occurring in hot springs at quite high temperature are called thermophytes. There are certain algae which are known to 0 tolerate the temperature up to 85 C e.g. few genera belonging to family Chroococcaceae and Oscillatoriaceae. Oscillatoria brevis, Synechococcus elongatus and Haplosiphon lignosum are some common examples of thermophytes which can survive up to a temperature of 70°C at which generally plant life is not possible. 10) Parasitic algae. Cephaleuros virescens which causes 'red rust of tea' is a striking example of parasitic algae and causes heavy damage to tea foliage. 4  Chlorochytrium and Phyllosiphon are other examples of parasitic algae. Polysiphonia festigata a member of Rhodophyceae is reported as semiparasite on Ascophyllum nodosum. 11) Symbiotic algae. Several members of Cyanophyceae grow in association with other plant and lichens exhibit good example of it. Almost all the plant groups are known to have symbiotic association with blue green algae e.g., Nostoc is found within the thalli of Anthoceros and Notothylas, Anabaena cycadeae is reported in the coralloid roots of Cycas, Anabaena azollae occurs in Azolla etc. The association of Chlorella with nitrogen fixing bacterium Azotobactor chrooccocum, and with that of certain species of Ceratophyllum and mosses are other examples of symbiotic algae. Structure of algal cell The cells constituting the algal thalli are basically of two kinds, prokaryotic and eukaryotic. The prokaryotic cells (Fig.2) which constitute thalli of cyanophyta (blue- green algae) have a cell wall which contains a specific strengthening component not found in the cell walls of other algae. The central nucleoid has many irregularly arranged fine strands of DNA. The chlorophyll-pigment is bound to photosynthetic lamellae or thylakoids which may be arranged in parallel layers in the periphery of the cytoplasm or form a network extending throughout the cell cytoplasm. They are not organised into grana. The chloroplasts are thus absent and so are the mitochondria, golgi body and endoplasmic reticulum. The ribosomes are, however, present. The nuclear division does not take place by mitosis and no cell plate is formed. Such simple cells of blue-green algae (and bacteria) which lack a nuclear membrane, mitochondria, and plastids and do not divide by mitosis are called prokaryotic. The cells constituting the thalli of all other algae excepting the blue- greens are called eukaryotic. The eukaryotic cell (Fig.3) has the same structure as is typical of the higher plants. The nucleus is separated from the cytoplasm by a distinct nuclear membrane. It has mitotic figures and divides by mitosis. The cytoplasm contains membrane bound chloroplasts or chromatophores, mitochondria, 5 golgi bodies and endoplasmic reticulum. Fig.2. Cell Structure of Cyanophyta Fig.3. Cell structure of green algae Algal pigments The colour of the algal thallus which varies in different classes of algae is due to the presence of definite chemical compounds in their cells. These are called the pigments; each pigment has its own characteristic colour. The particular colour that a thallus has is due to the predominance of one pigment in a combination of several others. For example brown algae have predominance of Fucoxanthin and phycophein while red and blue green algae have excess of phycoerythrin and phycocyanin pigments respectively. Each group of algae has its own particular combination of pigments and a characteristic colour which is not found in the other algal groups. The photosynthetic pigments in algae are of three kinds, namely, chlorophylls, carotenoids and phycobilins or biliproteins. The algal chlorophylls are characterized by green colour and in solution they show the phenomenon of fluorescence and emit red light. Chlorophyll pigments are fat soluble compounds and are of five different types. chlorophyll a, b, c, d, and e. Out of these chlorophyll a is universally present in all the groups of algae whereas chlorophyll b, c, d and e have restricted distribution. Chlorophyll a - present in all higher plants and algae. Chlorophyll b - present in all higher plants and green algae. Chlorophyll c - present in diatoms and brown algae and Chlorophyll d - present in red algae. 6 (Chlorophyll a is present in all photosynthetic organisms that evolve O2.) 2. Carotenoids are fat soluble yellow coloured pigments and are subdivided into carotene, xanthophylls and carotenoid acids. 3. Phycobilins are water soluble blue (phycocyanin) and red (Phycoerythrin) coloured pigments and are present in the members of Cyanophyceae and Rhodophyceae. Taxonomic Group Photosynthetic Pigments Cyanobacteria chlorophyll a, chlorophyll c, phycocyanin, phycoerythrin Green Algae (Chlorophyta) chlorophyll a, chlorophyll b, carotenoids Red Algae (Rhodophyta) chlorophyll a, phycocyanin, phycoerythrin, (phycobilins) chlorophyll a, chlorophyll c, fucoxanthin and other carotenoids Brown Algae (Phaeophyta) chlorophyll a, chlorophyll c, fucoxanthin and other carotenoids Golden-brown Algae (Chrysophyta) chlorophyll a, chlorophyll c, peridinin and other carotenoids Dinoflagellates (Pyrrhophyta) Algal flagella They are of two main types, whiplash (A) and tinsel (B). The whiplash flagellum has a smooth surface. The tinsel flagellum bears longitudinal rows of fine, minute flimmer hairs arranged along the axis almost to the tip of the flagellum. There may be a single row of hairs as in the Euglenophyta and Pyrrophyta or two as in Chrysophyceae and Phaeophyceae. The hairs arise from the margins of the peripheral fibrils. The whiplash or smooth flagella are also known by other names such as acronematic or peitchgeisel. The other names for the tinsel flagella are pantonematic, flimmer or flimmergeisel. The use of electron microscope has revealed a third kind of flagellum in which the 7 surface of the flagellum is covered by scales (Chara) and minute, short, stiff hairs. The hairs differ from those on the tinsel type. They can be easily detached. Flagellation The position, number and kinds of flagella on the motile cells are strikingly constant in each division of algae but differ from division to division. Thus it forms an important taxonomic feature for primary classification of algae. The blue –green and red algae lack flagella. The motile cells in green algae and stoneworts usually have two, rarely four equal flagella of whiplash type inserted at the anterior end (A and B) the only exception is the Oedogoniales in which the motile cells have a crown of flagella (C). The yellow green algae (Xanthophyceae) have two unequal anterior flagella. One of these is of whiplash type and the other tinsel (D). The diatoms (Bacillariophyceae) are characterized by a single tinsel flagellum on the male cell at the anterior end (E). In brown algae only the reproductive cells are motile. They are furnished with two unequal flagella. One of these is of tinsel type and other whiplash (F). Food reserves The food materials which accumulate as food reserves in the form of polysaccharides, however, vary from group to group and thus provide useful data for preliminary classification of algae. True starch is typical of only two algal divisions namely, Chlorophyta and Charophyta. The two other kinds of characteristic starches are the cyanophycean starch (Cyanophyta) and floridean starch (Rhodophyta). The three other important polysaccharides which accumulate as reserve food are laminarin found in the brown algae, paramylon characteristic of Euglenoids and leucosin peculiar to the Xanthophyta, Bacillariophyta and Chrysophyta. Besides, a proteinaceous compound cyanophycin is found only in the cells of blue-green algae. Mannitol which was formerly considered to be unique to the brown algae has recently been reported to 8 occur in a few red algae. Fats occur as reserve food in the cells of Xanthophyta, Bacillariophyta and Chrysophyta. Fig 4. Types of Algal flagella Factors affecting algal growth 1. Light The light of the important factors affecting the growth of algae in the waters of rivers and lakes and in rivers, but the light may be less often because of turbidity, which accompany the rivers, which lead to block the light from the sun except a thin layer of surface water. 9 2. Macronutrient Nutrients, major inorganic Macronutrient such as: a-phosphate. b-Nitrate. Are the major nutrients of the key factors that determine the number and types of algae, especially nitrates and phosphates and the element is added to the silica for the diatoms. 3. Temperature Various factions of algae for micro-, super- and optimal temperature in which to grow, for example, the optimum temperature for the growth of Diatoms ranging from 18-30 °C, while green algae thrive at temperatures ranging from 30-35 °C, and blue-green algae thrive at temperatures ranging between 35 -40°C. 4. Micronutrient Most algae grow best when the concentration of iron in the water ranges between 0.2 to 2 mg/l, while the observed toxicity of iron when the increased focus on the 5 mg/l. 5. Biological Factors: Biological Factors such as: a) Competition between aquatic organisms on nutrients. b) The rate of other organisms feeding on algae. Classification of algae The committee on the International Code of Botanical Nomenclature has recommended certain suffixes for use in the classification of Algae. These are phyta for division, phyceae for class, phycideae for subclass, ales for order, inales for sub- order, aceae for family, oideae for sub-family, Greek name for genus and Latin name for a species. Algal characteristics basic to primary classification. The primary classification of algae is based on certain morphological and physiological features. The chief among these are: (a) pigment constitution of the cell, (b) chemical nature of stored food materials, (c) kind, number, point of 10 insertion and relative length of the flagella on the motile cell, (d) chemical composition of cell wall and (e) presence or absence of a definitely organised nucleus in the cell or any other significant detail of cell structure. The details of vegetative structure and reproduction are useful for algal classification only at the level of families, genera and species. G.M. Smith (1955) divided algae into seven divisions, which were further subdivided into classes. The names of Divisions and classes are given below: Division 1: Cyanophyta/Myxophyta (Blue green algae-Prokaryotic algae). Represented by 1500 mostly fresh water species. Pigments are chlorophyll a ,C- phycocyanin and C-phycoerythrin and the reserve food is cyanophycean starch. Motile cells absent. Divided into a single class Myxophyceae e.g., Nostoc, Anabaena. Division 2: Chlorophyta includes about 5700 forms out of which 90% are fresh water and the remaining 10% are marine. Dominant pigments are Chlorophyll a and b, the reserve food starch. Divided into two classes: (l) Chlorophyceae (green algae) e.g., Volvox, Ulothrix; (2) Charophyceae (stoneworts) e.g., Chara. Division3: Euglenophyta includes 450 fresh water or terrestrial forms. Dominant pigments are chlorophyll and (3 carotene and reserve foods are paramylum and fats. Has been divided into a single class Euglenophyceae (the euglenoids) e.g., Euglena. Division 4 : Pyrrophyta include 1000 species mainly unicellular rarely colonial. Pigments are chlorophyll a & c, carotene and xanthophyll. Reserve foods is starch/oil. Divided into two classes: (1) Desmophyceae (dinophysids) e.g., Desmarestia', (2) Dinophyceae (Dinoflagelloids) e.g., Dinophysis Division 5: Chrysophyta represented by 6000 species of which 75% are freshwater and the remaining 25% marine. Dominant pigments are carotene and xanthophyll and reserve food is leucosin and oil. Divided into three classes: (1) Chrysophyceae (golden brown algae) e.g., Chromulina (2) Xanthophyceae (Yellow 11 green algae) e.g., Botrydium (3) Bacillariophyceae (diatoms) e.g., Pinnularia Division6: Phaeophyceae (Brown algae) represented by 1000 mostly marine forms, dominant pigments are phycophyein and fucoxanthin and reserve foods are laminarin and mannitol. Divided into three classes: (1) Isogeneratae e.g.Ectocarpus (2) Hetero generatae e.g., Myrionema and (3) Cyclosporae e.g., Sargassum Division 7: Rhodophyta (Red Algae) Includes 2500 species mostly marine. Predominant pigments are r-phycoerythrin. Reserve food is floridean starch. Division contains only one class Rhodophyceae e.g., Polysiphonia, Gracilaria, Batrachospermum (fresh water). Christensen (1964) proposed a new scheme of primary classification of algae into Procaryota and Eucaryota on the basis of difference between the Procaryotic and Eucaryotic cells. It is briefly given below: Reproduction In their methods of reproduction, the algae are as diverse as they are in the nature of the thallus. The primitive algae reproduce only by vegetative methods but in the higher forms both asexual and sexual reproduction are of common occurrence. The common methods of vegetative reproduction are by simple cell division, fragmentation and Hormogone formation. Asexual reproduction in algae takes place by different types of spores formed in favourable and unfavourable conditions by division of the protoplast. Zoospores are usually produced in favourable conditions whereas thick walled hypnospores are formed during adverse conditions. Other asexual spores which are formed in different groups of algae are aplanospores, autospores and endospores. Higher forms reproduce sexually which is an advanced method of reproduction in which fusion of two specialized cells known as sex-cells or gametes takes place. 12 Sexual reproduction may be isogamous in which two identical gametes fuse to form zygote or heterogamous in which the gametic union takes place between two dissimilar gametes having different size and behavior. Heterogamy is further divided in Anisogamy and oogamy. Fig.5: Vegetative reproduction: simple cell division and fragmentation A B C Fig. 6: Types of sexual reproduction in algae; A- Isogamy, B- Anisogamy and C- Oogamy respectively. Organisation of the thallus 13 The algae exhibit a great diversity in the organisation of the plant body. The simplest forms are motile or non-motile unicells (Chlamydomonas and Chlorella). In many species, the cells are grouped into aggregations called colonies e.g., Volvox and Pediastrun. These assume various forms and may be a hollow sphere, a flat plate or a filament. The filamentous types are usually multicellular and the filament may be simple e.g., Ulothrix, Zygnema or branched or an aggregation of filaments or a, highly organized thallus of a large size. In some multicellular forms the cells may perform both functions, vegetative and reproductive as in Oedogonium, while in others special reproductive cells or organs may be developed, e.g., Chara. My Best Wishes Prof. DR. Abla Farghl 14