313 ALGOLOY DERS NOTLARI

Doç. Dr. Muzaffer Dügel AİBÜ Fen-Edebiyat Fakültesi Biyoloji Bölümü

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İÇİNDEKİLER 1 INTRODUCTION TO THE ALGAE ................................................................................. 1

1.1 Classification ............................................................................................................... 1

2 MORPHOLOGY ................................................................................................................ 3

2.1 Biochemical and structural features of Algae .............................................................. 3

2.2 Range of Morphological Diversity in Algae ............................................................... 4

2.2.1 Unicellular organization ....................................................................................... 4

2.2.2 Colonial Organization .......................................................................................... 5

2.2.3 Filamentous organization ..................................................................................... 6

2.2.4 Siphonaceous organization ................................................................................... 7

2.2.5 Parenchymatous organization .............................................................................. 8

3 REPRODUCTION AND LIFE HISTORY ........................................................................ 9

3.1 Asexual reproduction of algae ..................................................................................... 9

3.2 Sexual reproduction of algae ..................................................................................... 11

4 CYTOLOGY OF ALGAE ............................................................................................... 14

4.1 Cell walls ................................................................................................................... 14

4.1.1 Coccoliths: .......................................................................................................... 14

4.2 Flagella ...................................................................................................................... 15

4.3 Plastids (chromatophore = chloroplast) ..................................................................... 17

4.4 Algal pigments ........................................................................................................... 17

4.4.1 Chlorophyll pigments ......................................................................................... 17

4.4.2 Carotenoid pigments .......................................................................................... 19

4.4.3 Phycobilin pigments ........................................................................................... 19

4.4.4 Chromatic adaptation ......................................................................................... 20

4.4.5 Endosymbiosis and origin of plastids ................................................................. 21

4.5 Pyrenoids ................................................................................................................... 23

4.6 Mitochondria ............................................................................................................. 23

4.7 Eyespots (stigma) ...................................................................................................... 23

4.8 Golgi apparatus .......................................................................................................... 24

5 DIVERSITY OF THE ALGAE ....................................................................................... 25

5.1 Algae in the marine habitat ........................................................................................ 25

5.2 The Algae of Freshwater ........................................................................................... 27

5.3 Algal blooms .............................................................................................................. 28

5.4 Terrestrial algae ......................................................................................................... 28

5.5 Human uses of algae .................................................................................................. 29

5.6 Variations in algal nutrition ....................................................................................... 29

5.7 Summaries of the nine algal phyla ............................................................................ 30

6 GENERAL FEATURES OF ALGAL DIVISIONS ........................................................ 33

6.1 Division CYANOBACTERIA (Blue-green algae) ................................................... 33

6.1.1 Habitat ................................................................................................................ 34

6.1.2 Nitrogen Fixation ............................................................................................... 34

6.1.3 Protoplast ............................................................................................................ 34

6.1.4 Motility ............................................................................................................... 35

6.1.5 Form ................................................................................................................... 35

6.1.6 Reproduction ...................................................................................................... 35

6.1.7 Akinetes .............................................................................................................. 36

6.1.8 Cyanobacteria and the origin of an oxygen-rich atmosphere ............................. 37

6.2 Division EUGLENOPHYTA .................................................................................... 38

6.2.1 Reproduction ...................................................................................................... 39

6.2.2 Euglenoid ecology .............................................................................................. 40

6.3 Division CRYPTOPHYTA ....................................................................................... 40

6.3.1 Ecology ............................................................................................................... 41

6.4 Division HAPTOPHYTA .......................................................................................... 42

6.4.1 Fossil record ....................................................................................................... 43

6.4.2 Thallus type ........................................................................................................ 44

6.5 Division DINOPHYTA (dinoflagellates) .................................................................. 45

6.5.1 Bioluminescence ................................................................................................ 46

6.6 Division OCHROPHYTA ......................................................................................... 47

6.6.1 Diatoms .............................................................................................................. 48

6.7 Division CHLOROPHYTA ....................................................................................... 48

6.7.1 Class: Charophycea ............................................................................................ 49

6.7.2 Order: Charales .................................................................................................. 49

6.7.3 Killer algae in the Mediterranean Sea ................................................................ 50

7 ECONOMIC ASPECTS .................................................................................................. 51

7.1 Agar ........................................................................................................................... 51

7.2 Alginic acid (alginate) ............................................................................................... 52

7.3 Diatomite ................................................................................................................... 52

7.4 Other aspect of using algae ........................................................................................ 53

7.4.1 Fertilizer ............................................................................................................. 53

7.4.2 Fodder ................................................................................................................. 53

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7.4.3 Food .................................................................................................................... 53

8 BIOLOGICAL ASSESSMENT IN WATER POLLUTION. .......................................... 54

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1 INTRODUCTION TO THE ALGAE From tiny single-celled species one micrometer in diameter to giant seaweeds over 50 meters long, algae (sing., alga) are abundant and ancient organisms that can be found in virtually every ecosystem in the biosphere. (The word alga is derived from Latin word for “seaweed”). For billions of years algae have exerted profound effects on our planet and its biota, and they continue to do so today. People from many cultures, ancient and modern, have used algae for a variety of purposes.

Although most algae are autotrophic, they are not considered plants because they lack many plant structures, such as roots, stems, and leaves. Algae lack a cuticle, which is a waxy covering over the aerial parts of plants that reduce water loss. When actively growing, algae are restricted to damp or wet environments such as the ocean; freshwater ponds, lakes, and streams; hot spring; polar ice; alpine snow; moist soil, threes, and rocks; and the bodies of certain animals, including sloths, sea anemones, corals, and worms. Also most algae do not have multicellular gametangia (sing. gametangium; reproductive structure in which gametes are produced). Algal gametangia generally are formed from single cells.

1.1 Classification The history of taxonomy at the kingdom level is a good example of the process of science. From the time of Aristotle to the mid 19th century, biologist divided organisms into two kingdoms: Plantae and Animalia. After the development of microscopes, it became increasingly obvious that many organisms could not be easily assigned to either the plant or the animal kingdom. For example, the unicellular organism Euglena, which has been classified at various times in the plant kingdom and in the animal kingdom, carries on photosynthesis in the light but in the dark uses its flagellum to move about in search of food. In 1886 a German biologist Ernst Haeckel, proposed that a third kingdom, Protista, be established to accommodate bacteria and other microorganisms such as Euglena. That did not appear to fit into the plant or animal kingdoms. Today many biologists place algae (including multicellular forms), protozoa, water molds, and slime molds in kingdom Protista. Table 1.1 Two super kingdoms and six kingdoms

Superkingdom Kingdom Characteristics

Prokaryota Eubacteria Lack distinct nuclei and other membranous organelles; unicellular; microscopic; cell wall generally composed of peptidoglycan; photosynthetic autotrophs, chemosynthetic autotrophs, and heterotrophs.

Archaebacteria Unicellular; microscopic: peptidoglycan absent in cell walls; differ biochemically from eubacteria. Methanogenes, extreme halophiles, extreme thermophiles. Strict anaerobes.

Eukaryota Protista Mainly unicellular or simple multicellular. Three informal groups. (not taxa) include protozoa; algae; and slime molds and water molds. Autotrophs, heterotrophs or both.

Fungi Heterotrophic; absorb nutrients; do not photosynthesize; cell walls of chitin

Plantae Multicellular; photosynthetic; possess multicellular reproductive organs; alteration of generations; cell walls of cellulose

Animalia Multicellular heterotrophs; many exhibit tissue differentiation and complex organ systems; most able to move about by muscular contraction; specialized nervous tissue coordinates response to stimuli.

In 1937 the French marine biologist Edouard Chatton suggested the term procariotique (“before nucleus”) to describe bacteria, and the term eucariotique (“true nucleus”) to describe all other cells. This dichotomy between prokaryotes and eukaryotes is now universally accepted by biologists as a fundamental evolutionary divergence.

Many biologists now group organisms into two superkingdoms and six kingdoms. The two superkingdoms are Prokaryota and Eukaryota. The six kingdoms are Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

A term of algae is not a taxonomical level but a group. Table 1.1 show all living things on the land, algae group are classified into kingdom Protista. We can put the photosynthetic Protista (all protists that possess plastids) within the algae group. Cyanobacteria (blue-green algae) are prokaryotic algae and taxonomically include in the Eubacteria kingdom.

The International Code of Botanical Nomenclature laid down the suffixes to be used for categories of plant classification and the following are those applicable to algae.

DIVISION (Phylum)—phyta SUBDIVISION—phytina CLASS—phyceae SUBCLASS—phycidae ORDER—ales SUBORDER—inales FAMILY—aceae GENUS (Normally a Latin name) SPECIES (Latin)

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2 MORPHOLOGY

2.1 Biochemical and structural features of Algae A number of characteristics have been traditionally used in distinguishing among the major algal groups. Leading among these are the types of photosynthetic pigments, nature of the cell covering, and the type of storages reserves present (Table 2.1)

Table 2.1 Predominant photosynthetic pigments, storage products, and cell wall components for the major algal groups

Cya

noba

cter

ia

Gla

ucop

hyta

Eug

leno

phyt

a

Cry

ptop

hyta

Hap

toph

yta

Din

ophy

ta

Och

roph

yta

Rho

doph

yta

Chl

orop

hyta

Photosynthetic pigments chlorophyll a ● ● ● ● ● ● ● ● ● chlorophyll b ● ● chlorophyll c ● ● ● ● phycocyanin ● ● ● ● allophycocyanin ● ● ● ● phycoeryhtrin ● ● ● ● α-carotene ● ● ● ● β-carotene ● ● ● ● ● ● ● ● ● xanthophylls ● ● ● ● ● ● ● ● ●

Storge products cyanophycin granules, ● cyanopytan starch (glycogen) ● ● starch ● paramylon ● chrysolaminaran ● lipids ● floridian starch ●

Cell covering peptidoglycan ● ● some cellulosic ● ● proteinaceous pellicle ● ● cellulosic plates ● CaCO3 scales common ● sulfated polysaccarides ● some calcified ● wall of cellulose ● some silica/organic scales ● ● some alginates ● some naked ● ●

2.2 Range of Morphological Diversity in Algae A great deal of variation exists in the morphology of the algal thallus (the algal body),

the most commonly encountered forms of which are described briefly in the following paragraphs.

Thallus Type in The Algae

1. Unicellular organization

Motile unicellular (Flagellate unicells)

Non-motile unicellular

Protococcoidal type

2. Colonial organization

Motile colonies (Flagellate colonies)

Non-motile colonies

Non flagellate coenobia

Rhizopodial type

Tetrasporal forms

3. Filamentous organization

Unbranched filaments

Branching filaments

4. Siphonaceous organization

5. Parenchymatous organization

2.2.1 Unicellular organization Simple isolated cells are found in all algal groups except the Charophyceae (a green alga) and Phaeophyceae (brown algae), while in some groups they are the only form represented e.g. Bacillariophyceae (an Ochrophyta). Some unicellular algae are nonmotile, while others possess one (or more) of the various means of locomotion found among the algae. Some algae have locomotory structures known as flagella.

Rhizopodial type: Rhizopodial cells lack rigid cell walls and form cytoplasmic projections; they are found in the Chrysophyceae (an Ochrophyta—golden-brown algae) Chrysamoeba (Figure 2.1a).

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(a)

(b)

(c)

Figure 2.1 Examples of the rhizopodial and Protococcoidal type of algae; (a) Chrysamoeba (rhizopodial), (b) Chlorella and (c) Micrasterias (protococcoidal)

Protococcoidal type: Some of the simplest non-motile genera are found in the Cyanobacteria, Synechoccus, which lacks even an organized nucleus and plastids while simple spherical cells with a nucleus and plastids containing the characteristic pigments of the group, occur in the Chlorophyta (Chlorella) (Figure 2.1 b,c)

Flagellate unicells: Motile vegetative cells, moving by means of flagella, are found in all groups except the cyanobacteria, Rhodophyta, Phaeophyceae, Charophyceae, and Bacillariophyceae (diatoms). With a few exceptions the structure of the flagellate vegetative cells, gametes and zoospores, is remarkably constant and characteristics. In the Chlorophyceae (Isokonte) the vegetative cells, the zoospores and the gametes, all have two equal flagella or multiples of two, in the dinophyceae there two unequal flagella running in different planes, in the Chyrsophyceae one or two and in the pigmented Euglenophyta one long, at least in some, one short (Figure 2.2).

Figure 2.2 A flagellate unicellular algae

(Phacus) (Euglenophyta)

2.2.2 Colonial Organization

(a) (b) Figure 2.3 Flagellate colonies (a) Gonium, (b) Volvox.

Flagellate colonies: Motile flagellate cells aggregate to form simple colonies in some species of Ceratium (Dinophyta); in this the unmodified cells form into chains after division. In the some green algae clusters of the cells, bearing siliceous scales or bristles are common. In the Chlorophyceae, aggregates of cells, embedded in mucilage, from either plate–like colonies

(e.g. Gonium) (Figure 2.3a) or mucilage spheres in which the cells are arranged just below the surface and are interconnected by protoplasmic filaments (e.g. Volvox) (Figure 2.3b).

Coenobia: If a colony assemblage of individual cells form predictable number and arrangement of cells remain constant throughout the life of the individual, this colony type is referred to as a coenobium. Depending on the organism, cells in coenobia may be either flagellated or nonmotile (e.g. Pediastrum) (Figure 2.4).

(a) (b)

Figure 2.4 Coenobial algae (a) Scenedesmus, (b) Pediastrum. Note that each colony compose of constant number of cells.

Tetrasporal forms: In most groups of algae, non-motile colonies are found in which the cells are embedded in mucilage; these are known as tetrasporal thalli. The name is came from Tetraspora (a green algae) in which the cells grouped in fours and no case in there any connection between these. Tetraspora is a large nonmotile colony. Rather than flagella, each cell of the vegetative colony bears two pseudocilia, which appear to have been evolutionarily derived from flagella by reduction. Pseudocilia cannot undergo swimming motions, and their function in Tetraspora and its relatives is unknown (Hata! Başvuru kaynağı bulunamadı.).

(a) (b) Figure 2.5 Tetrasporal forms; (a) Microcystis (blue - green algae) (b) Tetraspora with pseudocilia (green algae).

2.2.3 Filamentous organization Simple unbranched filaments are found in only a small number of algal groups; they may be either free-living (e.g. Ulothrix), attached at least initially (e.g. Oedogonium), or aggregated into colonies (e.g. Nostoc). In the cyanobacteria the filament (trichome) is formed of simple vegetative cells (e.g. Oscillatoria), the only modification being the development of the apical cell into a hooded or variously shaped cell. In Spirulina and sometimes in Anabaena, the filament is wound into a loose or close helix (Figure 2.6a,b)

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Branching filaments: In Cladophora, a sample branched system found with basal attachment cells. The branches of the former end in very characteristic hairs with bulbous bases and cell division is of the Oedogonium type. The Charales (e.g. Chara) have a complex branching system derived from apical cells which cut off segments at the base which form nodal and internodal cells (Figure 2.7).

Figure 2.7 Branched filamentous algae; (a) Cladophora (b) Chara

(green algae)

2.2.4 Siphonaceous organization This type of thallus is confined to a few genera in the Xanthopyceae. The simplest organization is that of a small unbranched vesicle containing a central vacuole and peripheral cytoplasm in which the chloroplasts and nuclei are located and anchored by branching rhizoid (Vaucheria) (Figure 2.8)

Figure 2.8 Siphonaceous Vaucheria (yellow-green

algae)

(a) (b)

(c) Figure 2.6 Unbranched filamentous algae; (a) Oscillatoria (blue-green algae), (b) Nostoc (blue-green algae), (c) Ulothrix

(green algae).

2.2.5 Parenchymatous organization Parenchyma is a term used to describe plant (or algal) tissue that is composed of relatively undifferentiated, isodiametric cells generated by a meristem. It results from cell divisions occurring in three directions, which gives rise to a three-dimensional form. Pseudoparencymatous algae have thalli that superficially resemble parenchyma, but which are actually composed of appressed filaments or amorphous cell aggregates.

Evolutionarily, parenchymatous growth habits are thought to represent the most highly derived state, with pseudoparencymatous forms representing an intermediate condition between filamentous and parenchymatous conditions.

Figure 2.9 Parenchymatous forms (the brown kelp

Macrocycstis).

Parenchymatous and pseudoparencymatous algae assume a wide range of shapes (sheets, tubes, stem- and leaf-like arrangements, etc.) and sizes (microscopic to lengths of 50 m or greater). Ulva (sea lettuce) and Macrocystis (giant kelps) are given for an example of parenchymatous algae. Macrocystic is reach 50 meter long and construct like a rain forest under the sea (Figure 5.1, Figure 2.9)

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3 REPRODUCTION AND LIFE HISTORY Algae reproduce by a variety of means, both sexual and asexual. In sexual reproduction, plasmogamy—fusion of haploid reproductive cells (gametes)—is followed by karyogamy (nuclear fusion), to form a diploid zygote. The homologous chromosomes contributed by each of two gametes pair and at some point are partitioned into haploid cells through the process of meiosis.

Asexual reproduction is a means by which an individual organism can produce additional copies of itself without such unions of cytoplasmic and nuclear materials or meiosis.

3.1 Asexual reproduction of algae In general its process the protoplast is released from the algal cell and germinates to form a new plant.

Cellular bisection: In unicellular flagellates (e.g. Euglena), in the desmids and diatoms, increase in size is controlled within fairly narrow limits. Division of the cell occurs when a set size is reached, e.g. in desmids (fam Desmidiaceae) which this size is related to the basic morphology of the cell. In multicellular algae (or colonies with indeterminate numbers of cells), this process would lead to growth of individual, i.e., an increase in the size and the number of its cells.

In diatoms, vegetative division is initiated after a period of increase in cell volume, accompanied by a growth and sliding apart of the girdle bands; the valves do not increase in size, and thus cell division is accompanied by a progressive reduction in cell size (Figure 3.1)

Hypotheca

Epitheca protoplast enlarge dividing protoplast completing the valves

Figure 3.1 Diagram of the process developing new valves produced after a diatom cell division. Note that reduction in the mean

cell size as the population increases through time.

In flagellates, vegetative reproduction is brought about by the longitudinal fission of the cell and the reformation of the organelles, which have not divided e.g. the eyespot. Fission usually starts at the anterior end and progress downward.

Zoospore and aplanaspore formation: Zoospores are flagellate reproductive cells that may be produced within vegetative cells or in specialized cells, depending on the organism (Figure 3.2d). Zoospores contain all of the components necessary to form a new individual. Sometimes, rather than forming flagella, the spores begin their development before being released from the parental cell of sporangium (Figure 3.2e). These nonmotile spores are termed aplanaspores.

Autospore or monospore production: Autospores and monospores are also nonmotile spores, but unlike aplanaspores, lack the capacity to develop into zoospores. Typically look like miniature versions of the parental cell in which they form (Figure 3.2f). In green algae, such cells are known as autospore; they are termed monospores in red algae.

(a) (b) (c)

(d)

(e)

(f)

(h)

(i)

(g)

separation disc

Hormogonia

Figure 3.2 Examples of asexual reproduction in the algae include (a)-(c) cellular bisection; (d) zoospore, (e) aplanaspor, and (f)

autospore production; (g) autocolony formation; (h) fragmentation; and (i) akinetes.

Autocolony formation: In coenobia, each cell goes through a consistent number of successive divisions giving rise to a miniature version—an autocolony—of the original coenobium (Figure 3.2g). Depending on the organism, autocolonies may be formed from nonmotile or motile cells that arrange themselves in a pattern identical to that of the parental cells.

Fragmentation: The simplest methods of the asexual reproduction are those in which division of the protoplast is not directly involved, but where the individual cells or cell-aggregates are separated. In Cyanobacteria, Ulatrichales and filamentous Zyngnemaphyceae, fragmentation of filaments occurs. In these filamentous groups, sections of trichomes are cut off by the occurrence. The short lengths of trichome thus released are known hormogonia and are often more actively motile than the parent filament (Figure 3.2h). They arise by separation of adjacent terminal walls in the tirchome or by the death of certain cells that may become concave separation disc or necridia

Akinetes: An akinete is a vegetative cell that develops a thickened cell wall and is enlarged, compared to typical vegetative cells (Figure 3.2i). It is usually a resistant structure with large amounts of stored food reserves that allow the alga to survive unwanted environmental conditions, germinating when they improve. Rather than a means of producing additional

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copies of the individual during active growth, akinetes represent a type of survival mechanism.

3.2 Sexual reproduction of algae Sexual reproduction is not a universal feature in the algae; it has been never demonstrated in the Cyanobacteria and in many genera of the Chrysophyta and Bacillariophycea it has rarely been observed, although it is probably a feature of the life history of most species.

Gametes and gamete fusion: Sexual reproduction involves the combination of nuclear material and frequently cytoplasm, from two organisms of the same species. The commonest mechanism is the union of two morphologically identical gametes (isogamy). The gametes may be motile and similar size and shape fuse with each other. In some species the gametes differ in size or in motility (anisogamy), and in these the larger or less active gamete generally absorbs the other. The oogamous state is achieved when one gamete becomes immobile; this egg cell may be released (e.g. Fucus). Oogamy occurs more widespread in Phaeophyta (brown algae) and Rhodophyta (red algae). Another type of fusion is illustrated by some diatoms in which daughter nuclei fuse without release from the parent cell (autogamy).

Life history types: The union of male and female gametes results in the formation of a zygote and a doubling of the chromosomal complement to give the diploid state. Before reproduction can occur again the chromosome number must be halved. There is a three type of life histories depend on where the meiosis occurs and the type of cells it produces, and whether or not there is more than one free-living stage present in the life cycle.

Characteristics of the three types are:

1. The major portion (vegetative phase) of the life cycle is spent in the haploid state, with meiosis taking place upon germination of the zygote (zygotic meiosis) (Figure 3.3).

2. The vegetative phase is diploid, with meiosis giving rise to the haploid gametes (gametic meiosis) (Figure 3.4).

3. Two or three multicellular phases occur—the gametophyte (typically haploid) and one (or more, in the case of many red algae) sporophytes (typically diploid). The gametophyte produces gametes through mitosis, and the sporophyte produces spores through meiosis (sporic meiosis). This type of life cycle illustrates the phenomenon of alteration of generations. Alteration of generations in the algae can be isomorphic, in which the gametophyte and sporophyte are structurally identical, or heteromorphic, where gametophyte and sporophyte phases are dissimilar (Figure 3.4).

The first life-cycle types are termed haplobiontic (one type of free living individual) the second type, diplobiontic (two free living stages) and the final type diplohaplontic (two phases, (diploid and haploid) life cycle. To ovoid the use of what can be confusing, similar sound terms (haplobiontic, haplontic, haploid, etc.), we can distinguish these life cycle types by the nature of meiosis (zygotic, gametic, sporic), with the realization that theses terms are inconsistent in that zygotic refers to the place where meiosis occurs, while gametic and sporic refer to the nature of the meiotic products.

gametes

zygote

fertilization

vegetative cells

N

2N

-

+

+

-

Z

meiosis

mei

osis

Figure 3.3 Zygotic meiosis in the green unicellular flagellate Chlamydomonas.

antheridium oogonium

zygote

egg

mei

osis

2N N

sperm

G

mei

osis

Figure 3.4 Gametic meiosis in a monecious species of the brown rockweed Fucus.

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ferti

lizat

ion

mei

osis

+ gametophyte

- gametophyte

gametes

+

-

spores

sporophyte

2N N zygote

mei

osis

S

Figure 3.5 Sporic meiosis in the green alga Ulva. Note that there are two free-living multicellular stages, one haploid one diploid

(alteration of generations).

4 CYTOLOGY OF ALGAE The details of algal cytology have increased enormously during the last two decades largely from electron microscope studies of cell walls, flagella and cytoplasmic organelles. The ultra-structural studies are also proving invaluable in solving problems of classification and inter-relationships of groups.

4.1 Cell walls A cell wall of an algae composed of relatively pure or mixed carbohydrates. Sometimes this structure layered with inorganic substances, e.g. silica, calcium or magnesium carbonate.

In many flagellates, zoospores and gametes the enclosing membrane is merely the outermost layer of cytoplasm (pellicle, periplast). In some algae it is quite flexible, allowing amoeboid or rhizopodial motion, while in others it has a more definite form owing to underlying structural elements like Euglena. Even in Euglena there is often considerable change in cell shape (metaboly) appearing as an inflation passing up and down the cell. In spite of the cytoplasmic nature of this type of cell membrane, it may have extremely complex striations, be produced into wings, or be ornamented with a spiral system of nodules.

In most non-motile, unicellular and all the multicellular species the cytoplasm is bounded by a definite cell wall; it is rarely composed of a single substance and usually has a layered structure. The outer layer is often mucilaginous or is a thick envelope of mucilage, not normally visible.

A common constituent of algal cell walls is pectin, but it is more frequently mixed with cellulose (Chlorophyta, Dinophyta, Rhodophyta, Phaeophyta), with xylose and/or mannose (Bryopsidophyceae) or silica (Bacillariophcea). In some algae the wall is strengthened with plates or an encrusting and even penetrating deposit of calcium carbonate (Coccoliths) (coralline Rhodophyta, Coccolithinae).

4.1.1 Coccoliths: The scale and coccoliths of the Prymnesiales (a section of the haptophyta), are outer small, that only electron micrographs reveal the full detail.

Figure 4.1 SEM view of Emiliana huxleyi, showing the coccosphere made up of intreloking coccoliths.

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There are two main types of coccolith.

1. Holococcoliths: They are composed of submicroscopic crystals. They are formed extracellularly.

2. Hetercoccoliths: These are the larger, more obvious coccoliths built up of plates, ribs, etc., to form a complex amorphous structure (e.g. Emiliana huxleyi, Figure 4.1)

The formation of either holococcoliths or heterococcoliths may in some instance be a valid taxonomic criterion. The mechanism of coccolith formation is not yet completely understood but there is evidence that in Coccolithus and Criscosphaera the unmineralised scales and calcareous coccoliths arise within the bladder of Golgi body. The function of these complex calcareous plates is unknown. Superficially it would appear that this “heavy skeleton” would be detrimental to floating organisms. Emiliana huxleyi is a haptophytean can be given as example for coccolith formation.

Coccoliths probably serve a number of functions, including restriction of access to cells by pathogenic bacteria and viruses, protection from predation by protozoa, and buoyancy regulation (by regulated production/loss of heavy coccoliths).

4.2 Flagella The flagella of algal cells differ in their place of insertion on the cell and in their number, length, and appendages.

Flagellum consists of two central microtubules surrounded by nine peripheral microtubules (axoneme) all enclosed in a plasma membrane. This structure is the basic pattern of plant and animal flagella. The flagella end in the cell, in hollow basal bodies separated from the flagellum by a diaphragm, but with nine outer tubules continued into wall while the two centre tubules stop short at the diagram.

Flagella types:

1. Acronematic flagella: This flagellum lacking hair-like appendages (smooth) and its ended by a fine hair. Acronematic flagellum is usually directed in posterior direction.

2. Pleuronematic flagella: Flagellum bearing lateral hair-like appendages (mastigonem) and is usually directed in an anterior direction. Pleuronematic flagella are known to be characteristic of Euglena, Cryptomonas, Synura, Vaucheria.

When these hairs arise unilaterally from the flagellum it is said to be stichonematic; if the mastigonems arranged in two rows, the term pantonematic is applied. The second flagellum, when present, is always of the acronematic type.

Stichonematic Pantenomatic Acronematic Two flagellum

The flagella of motile cells of most algae have different flagella compositions. If flagella are equal in length, it’s called isokont flagella. When these flagella unequal in length it is said to be heterokont flagella.

3. Haptonema: In some mainly marine flagellates, e.g. Chrysochromulina, there is in addition to the flagella, a structure known as haptonema, which is similar in length to the flagella or in some species much longer and often with a swollen tip; it is capable of boing coiled to varying degrees, even right up to the body in the form of a solenoid, is thinner than the flagella and can serve to anchor the flagellate. Haptonema consists of three concentric membranes enclosing a ring of six tubules; the outer is three-layered, each layer being approximately 3 nm thick, while the inner are thinner.

Typical eukaryotic flagellum showing

9+2 patterm

Haptonema cross section

Haptonema

Axonem

Chrysochromulina chiton (Chrysophyta)

The type of flagellum appears to be characteristic of taxonomic groups and constant throughout the group, e.g. one acronematic and one pleuronematic in the Phaeophyta and Xantophyta and two acronematic in the Chlorophyta. In the Chrysophyta the flagella bear mastigonems while those of the Haptophyta are smooth.

Basal region

Flagellu

Nucleus

a b c d e

f g h Figure 4.2 Behaviour of basal region and flagella during meiosis

a) A cell with flagellum b) withdraw flagellum into protoplasm c) Disappearing of axonema d) Bazal region goes near to nucleus e) Dividing of basal area f) Anaphase g) Telophase h) Construction of axonema

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4.3 Plastids (chromatophore = chloroplast) The most obvious feature of algal cells is the plastid, the form of which is a useful criterion of taxonomic affinity when combined with other features. Shape of chromathophores may be discoid, plate, simple, lobed, spiral, branched or very complex structure. Electron microscopic studies show a chromatophore membrane of unit membrane structure. Inside the chromatophore membrane further stacks of membranes occur, each of which is a paired structure, joined at the ends form thylakoids. In Rhodophyta, Chlorophyta and Charophyta chromotophore membrane consists of two layers, other algal eucaryotic algal groups in addition to this two layer there is a chloroplast endoplasmic reticulum (CER). The CER is an evagination of the outer nuclear membrane, extending to surrounds the chloroplasts and also pyrenoid, if present.

Thylakoids are the photosynthetic lamella which chlorophyll containing structures and granules, lipid droplets and starch grains are found in the matrix. Between the thylakoids is the matrix (or stroma) and this, the stacks of thylakoids and the membrane, form the algal chromatophore. In most algae there are no grana comparable to those of the higher plants, but in the desmid. Thylakoids are central of the photosynthetic reactions. They are the sites of chlorophyll a. In Cyanobacteria and Rhodophyta accessory pigments also occurs in thylakoid surfaces in the form of small particles, the phycobilisomes. In most algae the eyespots and pyrenoids are associated with plastids.

4.4 Algal pigments Algal pigments can be divided into three groups, differing widely in chemical composition.

Chlorophylls

Carotenoids (carotenes and xantophyllls)

Phycobilins

4.4.1 Chlorophyll pigments Fat soluble chlorophylls are tetrapyrrolic molecules with a central magnesium atom and two ester groups. Five chlorophylls have been isolated but only one, chlorophyll a, is common to all algal groups. There is a similarity between Chlorophyta and higher plants (which have only chlorophylls a and b). Chlorophylls are characterized by strong absorption of red (650-680 nm) and blue (400-450 nm). The chlorophyll molecule is loosely associated with protein molecules in the plastids.

Chlorophyll a is the main photosynthetic pigment that initiates the light-dependent reactions of photosynthesis. Chlorophyll b is an accessory pigment that also participates in photosynthesis. It differs from chlorophyll a only in a functional group on the porhpyrin ring: the methyl group (—CH3) in chlorophyll a is replaced in chlorophyll b by a terminal carbonyl group (—CHO). This difference shifts the wavelengths of light absorbed and reflected by chlorophyll b, making it yellow-green, whereas chlorophyll a is bright green.

chlorophyll a (reaction center)

incoming light Accessory pigments

Figure 4.3 Energy from photons bounces among pigment molecules until trapped by chlorophyll a molecule.

CH3 CH2

CH3 CH2

CH3

CH3

CH3

CH3 CH3 H CH3 H CH3

C

CH3

H H

N

H

O

CH2

OCH3 O

CH2

C

CHO

O O

H

N

N N

Mg

in chlorophyll a in chlorophyll b

Porphyrin ring (absorbs light)

Hydrocarbon side chain

Figure 4.4 Chlorophyll structure. Chlorophyll consists of a porphyrin ring and a hydrocarbon side chain. The porpyrin ring, with a magnesium atom in its center, contains a system of alternating double and single bonds: these are commonly found in molecules that strongly absorb visible light. At the top right corner of the diagram methyl group (—CH3) distinguishes chlorophyll a from chlorophyll b, which has a carbonyl group (—CHO) in this position.

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4.4.2 Carotenoid pigments The other fat-soluble group of pigments comprises the yellow- or red- colored carotenoids, consisting of carotenes, xantophylls (oxycarotenes) and carotenoid acids. They absorb blue and green light (430-500 nm). Transmit yellow and red, and are weakly fluorescent. Carotenes are unsaturated long-chain hydrocarbon molecules. The structure is a polyene chain, i.e. having alternate double and single bonds; light absorption is due to these bonds and the greater the number of double bonds the redder color. The ends of the chains of molecules are coiled into rings and like the chlorophylls they are loosely bound with proteins in the plastids. The β-carotene content of algae is generally less (5-20 percent) in the Chlorophyta than in the higher plants (30 percent of total pigment). β-carotene occurs in nearly all photosynthetic algae, and is particularly important as the main source of provitamin A, required by animals for synthesis of the visual pigment rhodopsin and in the regulation of genes involved in limb and skin development. These pigments harvest blue wavelengths of light that are not directly absorbed by chlorophyll a. In addition, carotenoids also provide protection from harmful photooxidation. Their association with chlorophyll prevents the formation of highly reactive oxygen radicals that could otherwise cause irreparable damage to lipids, proteins, and other molecules.

The xanthophylls are long chain hydrocarbons of the carotene type but with oxygen atoms forming hydroxyl (—OH) structures (Figure 4.5c).

CH3

CH3 CH3 CH3 CH3

CH3 CH3 CH3

CH3

CH3

β-carotene

CH3 CH3

CH3

CH3 CH3 CH2-OH

provitamin A

(a)

(b)

CH3

CH3 CH3 CH3

CH3 CH3

CH3 CH3

CH3 CH3

OH

OH

(c) zeaxanthin

Different from β-carotene

Figure 4.5 Structures of (a) β-carotene, (b) provitamin A, and (c) zeaxanthin. Provitamin A is formed by splitting β-carotene into two equal parts (at arrow). Zeaxanthin is a common xanthophyll, and is also synthesized from β-carotene.

4.4.3 Phycobilin pigments A group of water-soluble pigments (phycobilins) are found in the Rhodophyta, Cyanobacteria, and Cryptophyta. There are two types of phycobilins:

Phycocyanin: Transmitting blue light and absorbing green, yellow and red.

Phycoeryhtrin: Transmitting red light, and absorbing blue green and yellow.

Allophycocyanin: Transmitting and absorption features such as Phycocyanin but structurally different

Phycobilin pigments found in the phycobilisomes—located on thylakoids— captured light energy is efficiently passed to phycocyanin and allophycocyanin, and finally to chlorophyll a, allowing the harvesting of light energy of light energy that is otherwise inaccessible to chlorophyll. The components of phycobilisomes are arranged in such a way as to maximize energy transfer to chlorophyll a. On the basis of absorbance characteristics, energy transfer is expected to occur from phycoeryhtrin to phycocyanin to allophycocyanin to chlorophyll a in photosystem II (Figure 4.8)

Models of the structure of a phycobilisomes show an outer surface consisting of fingerlike stacks (rods) composed of several phycoeryhtrin molecules, an inner layer of phycocyanin, and a core of allophycocyanin molecules.

Any algae group (e.g. cyanobacteria) having chlorophyll b do not produce phycobilin pigments.

4.4.4 Chromatic adaptation Some cyanobacteria can adjust their pigment composition in response to changes in light quality. Exposure to red light increases synthesis of the blue-colored phycocyanin, whereas exposure to green light increases synthesis of phycoeryhtrin. Than some cyanobacteria can undergo a color change to red under green light, and change to blue-green pigmentation in red light. Such alteration of pigment composition, known as chromatic adaptation, provides an adaptive advantage to cyanobacteria whose light environment may change over their lifetime.

Light energy is passing through water is differentially absorbed, the red first then green and finally blue, so that the Rhodophyta (red algae), living generally at the greatest depth, have their maximum absorption in the green, which is the only light energy available in any quantity at such depth; the intermediate Phaeophyceans (brown algae in phylum Ochrophyta) absorb green-yellow-orange, which penetrates to intermediate depths and the Chlorophyta in the blue and red, both of which are available at the surface.

thylakoid

phycocyanin allophycocyanin phycoeryhtrin

Figure 4.6 A model of the phycobilisomes. Note the positions of the there types of phycobilin pigment molecules relative to the energy transfer incated in the figure The pigments are held together by linker proteins (striped boxes).

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Chlorophyll b

Chlorophyll a Carotenoids

Wavelength (nm)

400 500 600 700

1.0

0.8

0.6

0.4

0.2

Abs

orba

nce

Figure 4.7 Absorption spectra for chlorophyll

a, carotenoids, and chlorophyll b. The latter two pigment types act as “accessory” pigment, absorbing additional wavelengths of light and passing the energy along to chlorophyll a.

PHYCOERYTHRIN (A 545nm — F 575nm)

PHYCOCYANIN (A 555nm — F 636nm)

ALLOPHYCOCYANIN (A 650nm — F 636nm Aggregated F 675nm)

CHLOROPHYLL a (A 670nm — F 685nm)

hv

Figure 4.8 In phycobilisomes light energy is transferred from phycoeryhtrin to phycocyanin to allophycocyanin to and finally to chlorophyll a in thylakoids.

4.4.5 Endosymbiosis and origin of plastids We have two definition of symbiosis, one of them is original definition “living together of dissimilar organisms” and a more modern one, “living together in physical contact of organisms of different species” as well as extending the definition to intracellular associations.

Phagotrophy (the ingestion of particulate food) is regarded as the major mechanism by which algal plastids were acquired, and it has been proposed that the earliest photosynthetic eukaryotes in all of the major algal lineages were phagotrophic.

The process of incorporation and integration of bacterial endosimbiyonts (photosynthetic cyanobacteria blue-green algae) within host cells to form ekaryotic, organelle-containing

entities is called primary endosymbiosis (Hata! Başvuru kaynağı bulunamadı.) The process by which eukaryotic cells are taken up and integrated into host cell is known secondary endosymbiosis (Hata! Başvuru kaynağı bulunamadı.). Red algae (Rhodophyta) and green algae (Chlorophyta) have plastids that arisen by primary endosymbiosis. Their plastid structure supports this theory. They have only two layer of membrane, but the other algal groups have more than two layers. Algal groups those plastids arisen by secondary endosymbiosis evolved from red algae or green algae.

Following structure of plastids supports endosymbiosis theory.

1. The DNA of algal plastids has ring shaped nucleotids. The plastid transcription and translation system is very similar to that of bacteria.

2. Ribosomal sizes (70 S) and the spectrum of antibiotic sensitivities very similar to tahat of bacteria.

3. Membranes of plastids compose of more than one layer.

Similarities in plastid and eubacterial structures indicate that all modran plastids are of cyanobacterial origin.

N

N

free-living bacterium

phagotrophic eukaryote

Mitochondrion or

plastid

N

C

photosynthetic prokaryote

phagotrophic eukaryote

photosynthetic eukaryote/

primary plastid

2nd phagotrophic eukaryote

2nd photosynthetic eukaryote /

secondary plastid

C N

N'

N'

N

Figure 4.9 A diagrammatic representation of the process of

primary endosymbiosis, in which a free living bacterium is incorporated into a phagotrophic eukaryotic cell and eventually transformed into an organelle.

Figure 4.10 Diagram of secondary endosymbiosis, whereby a eukaryote that earlier acquired a plastid via primary endosymbiosis is itself taken up by a second eukaryote.

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4.5 Pyrenoids In most algae pyrenoids are associated with the chromatophores. In most green algae the plastids contain one or more specially differentiated regions called pyrenoids. In the green algae the pyrenoid is the site of the starch formation, one or more starch grains forming within the chloroplast closely appressed to the surface of the pyrenoid. It has been suggested that the pyrenoid is the region of temporary storage for early products of photosynthesis that, upon overproduction, are converted into starch.

4.6 Mitochondria Mitochondria are basically similar in all groups, and certainly function similarly as sites of enzyme action in Krebs cycle, amino acid intreconversion and protein synthesis. They are bounded by a double membrane, the inner produced into folds (cristae), projecting into the lumen which contains a structureless or slightly granular matrix. In certain cells the number of mitochondria appears to be relatively constant. Cells of Cyanobacteria do not posses mitochondria.

Among the various algal groups, three types of mitochondria have been noted; they are distinguished by morphology of the cristae (Table 4.1). Some algal groups (ochrophytes, dinoflagellates, haptophyta) have mitochondria with tubular cristae, whereas others (glaucophytes, cryptomonads, red algae, and green algae) have flattened, plate-like cristae, while euglenoids have discoid cristae. It has been proposed that the mitochondrion arose once in common ancestor of all extant eukaryotes, possibly at the same time as the nucleus.

Mitochondria have long been known to posses eubacterial-like DNA and transcription and translation systems, including similarly sized ribosomes. Also, infoldings of the cell membrane similar to the cristae of mitochondria characterize certain alpha proteobacteria (purple bacteria), where they function in photosynthesis. These similarities, together with comparative molecular sequence evidence, particularly for 70 S ribosome genes, strongly support the hypothesis that mitochondria were once free-living photosynthetic proteobacteria that became endosymbiotically incorporated into the host cells, lost photosynthetic capacity, and assumed the specialized function of aerobic respiration.

Table 4.1 Characteristics of the mitochondria and endosymbiotic origin of plastids of the major eukaryotic algal groups

Group Mitochondrial cristae Plastid origin(s)

Glaucophytes (Glaucophyta) flattened primary

Cryptomonads (Cryptophyta) flattened secondary (red)

Red algae (Rhodophyta) flattened primary

Green algae (Chlorophyta) flattened primary

Euglenoids (Euglenophyta) disk-shaped secondary (green)

Haptophytes (Haptophyta) tubular secondary (red)

Dinoflagellates (Dinophyta) tubular mainly tertiary (various sources)

Ochrophytes (Ochrophyta) tubular secondary (red)

4.7 Eyespots (stigma) Many motile algae have eyespots. Eyespot may detect the direction of the source of light and distinguish light intensity. The eyespot of some flagellates is situated beneath the chromatophore membrane. It consists of clusters of carotenoid-lipid granules each surrounded

by a membrane. The eyespot of Euglena is not within the chromatophore, a feature which can be seen by light microscopy. Euglena eyespot granules also containing a special pigment (astaxantin). Astaxanthin (derivative of β-carotene) is a pigment occurring in several animals. This pigment characteristic of Euglena gives a special structure that both plants and animals.

4.8 Golgi apparatus These are present in all algal cells except Cyanobacteria and are fairly easily recognizable in sections under the electron microscope. They may be found in the region of the nucleus (e.g. in Chlamydomonas) or associated with flagellar basis (e.g. in Chrysochromulina) and are composed of stacks of flat vesicles. They are frequently accompanied by smooth, circular or oval vesicles which form at the edges of the dictiyosome. The Golgi apparatus of diatoms produce vesicles which are involved in wall formation. Heterococcolids of Haptophyta body wall formed internally by the Golgi apparatus. Bioluminescent dinoflagellates posses’ spherical structure derived from the Golgi apparatus. These vesicles contain luciferin, luciferas and some cases luciferin-binding protein.

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5 DIVERSITY OF THE ALGAE

5.1 Algae in the marine habitat On land the largest and most striking plants are the trees. Together with their herbaceous relatives, their foliage makes green the most conspicuous color of the biosphere. Underwater there are “trees” of similar height that are less widely valuable because most humans spend little time in their world. Brown undulating forests of 50-meter long giant kelps, as tall and crowded as their terrestrial counterparts, dominate significant stretches of submerged temperate coastlines. Like trees, kelps use photosynthesis

Figure 5.1 Kelp forest off the Chilean coast. Predominant alga pictured is Macrocystis sp.

To convert the energy of sunlight into chemical energy, but the green of their chlorophyll is masked by the large amounts of brown pigments. These accessory pigments aid in the collection of light not absorbed directly by chlorophyll molecules and channel the light energy to chlorophyll a (the only pigment that is able to effectively convert energy of absorbed light into high energy bonds of organic molecules. This is necessary because as light passes through water, the longer wavelengths are filtered out first, such that eventually all that remains is a faint blue-green light that cannot be absorbed by chlorophyll. The depth record for algae is held by dark purple-colored crusts of yet unnamed red algae discovered in tropical waters by phycologists using submersibles. These organisms live at depth greater than 250 meters, where the light intensity is only 0.0005% that of surface light. The accessory pigments of these algae are essential for the survival of photosynthetic in such low-irradiance environments. In contrast, algae that live in high-irradiance habitats typically have pigments that help protect against photodamage. It is the composition and amounts of accessory and protective photosynthetic pigments that give algae their wide variety of colors and, for several algal groups, their common names such as the brown algae, red algae, and green algae. But attempting to identify a particular alga by color alone could be problematic,

since, for example, there are red-colored green algae and brown of purple-colored red algae; other characteristics and features must also be considered.

The rocky or sandy shallows of temperate and tropical oceans harbor a vast array of brown, red, and green algal growths that many form thin and sometimes slippery films on rocks; or miniature jointed shrubs armored with limestone. Tropical corals share the sea bottom with intracellular tenants (microscopic golden algal cells known as zooxanthellae) that generate food and oxygen in exchange for metabolic by-products (carbon dioxide and ammonia) released by coral cells. Zooxanthellae help to corals to live in the typically low-nutrient conditions of tropical waters. Because of their obligate association with these photosynthetic algae, reef-building corals are limited to shallow, well illuminated waters less than 20meters or so in depth.

Figure 5.2 Hydra containing endosymbiotic green algae known as zoochlorellae.

Beneficial algae also occur within the cells and tissues of wide variety of other marine animals such as nudibrahchs, anemones, giant clams, ascidians, and sponges, as well as inside the cells of simple organism known as protists.

Algal aggregations and other large group of algae construct importance level of phytoplankton (free-living organisms that lack of swimming organelles). Although individually visible to humans only with the aid of a microscope, large populations can give ocean waters green or rusty colors. Color variations reflect differences in the types and amounts of blue-green, red, orange, and golden accessory pigments accompanying the green of chlorophyll.

Population of marine phytoplankton can become so large that they are detectable by satellite remote sensing technology. Such blooms are in fact one of the more dramatic vegetational features of the planet when viewed from space. Collectively marine microalgae have been modifying the earth’s atmosphere for more than 2.7 billion years, and they continue to exert a powerful influence on modern atmospheric chemistry and biochemical cycling of carbon, sulfur, nitrogen, phosphorus, and other elements. Hundreds of millions of years’ worth of past phytoplankton growth and sedimentation have generated important oil and limestone deposits. Species of Halophyta phylum generated chalk cliffs with their calcium carbonate coccoliths during Late Cretaceous and the name of time “Cretaceous” (chalk era) come from algae that lived during those times.

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5.2 The Algae of Freshwater Freshwater lakes, ponds and streams contain planktonic and attached forms microalgae.

(a)

(b)

Figure 5.3 Some freshwater algae. (a) Chara sp., a green alga commonly called a stonewort, is closely related to plants. Chara is widely distributed in fresh water, where it grows to 30 cm or longer. (b) LM of a widely distributed desmid (Micrasterias sp.), a unicellular green alga with mirror-image halves. (c) LM of Volvox colonies, each composed of 50.000 cells. New colonies can be observed inside the paternal colonies, which eventually break apart to release them.

(c)

The life form of algae according to their environment and features

Planktonic: free-floating, or suspended in the water column.

Benthic: Having to do with the benthos—the bottom of a lake, stream or marine system.

Epiphytic: living on the surfaces of plants or algae.

Epilithic: living on the surfaces on rocks.

Epipelic: living on the surfaces of mud or sand.

Epizooic: living on the surface on animals.

Endozooic: living within an animal’s body.

Although not exhibiting the huge size range of their marine relatives, freshwater algae display a wide diversity of form and function. As in the oceans, it is not uncommon to find that certain photosynthetic freshwater algae colonize the cells and tissues of protozoa or coelenterates like the familiar Hydra. Cyanobacteria living within the tissues of water ferns

can be a major to the nitrogen economy of rice cultivation in paddies and influence the nutrition of millions of human beings. Freshwater phytoplankton and periphyton (also known as benthic algae) form the base of the aquatic food chain, without which freshwater fisheries could not exist. In addition to oceanic and freshwater environments, some algae have adapted to extreme habitats such as hot springs and salty lakes

5.3 Algal blooms Blooms of microscopic algae occur in marine and freshwaters, often in response to pollution with nutrients such as nitrogen and/or phosphate. Nutrient pollution can usually be traced to human activities, such as discharge of effluents containing sewage or industrial wastes, or the use of agricultural fertilizers. Water transparency may become so reduced that organisms such as corals, aquatic plants, and periphyton no longer receive sufficient light for photosynthesis. It has been estimated that 50% or more of marine and freshwater algal blooms produce poisons that effect neuromuscular systems, are toxic to the liver, or are carcinogenic vertebrates. These toxins can cause massive fish kills, death of birds, cattle, dogs and other animals, and serious illness, or death, in humans.

(a) Figure 5.4 Algal blooms (a) in pacific ocean consisting a

dinoflagellate Noctiluca (b) in the Gippsland Lakes (Australia) consisting Nodularia spumigens, cyanobacteria.

(b)

5.4 Terrestrial algae A considerable number of algae have adapted to life on land, such as those occurring in the snows of mountain ranges, in “cryptobiotic crusts” typical of desert and grassland soils, or embedded within surfaces of rocks in deserts, polar regions and other biomes. The activities of soil and rock algae are thought to enhance soil formation and water retention, increase the availability of nutrients for plants growing nearby, and minimize soil erosion.

Several species of terrestrial algae, together with fungi, form the distinctive life-forms known as lichens. Lichens are ecologically important because of their role as pioneers in early stages of succession, where they help to convert rock into soil, slowly dissolving it with excreted acids. Lichens also help to stabilize fragile desert soil and are used as living barometers of air quality because of their sensitivity to air pollution.

Some terrestrial algae occur in surprising places. For example, algae can impart a greenish cast to the fur of giant sloths and sometimes live within the hollow hairs of polar bears. Also

29

pink color of flamingos is due to a red-colored algal accessory (carotenoid) pigment consumed as they feed. Algae also occur regularly within the tissues of various plants.

5.5 Human uses of algae For millennia people throughout the world have collected algae for food, fodder (food for farm animals), or fertilizer. More recently algae have begun to play important roles in biotechnology. For example, they have been used to absorb excess nutrients from effluents, thereby reducing nutrient pollution in lakes and streams. Algae also generate industrially useful biomolecules, and serve as a human food source, either directly or indirectly, by supporting aquaculture of shrimp and other aquatic animals.

Algae have provided science with uniquely advantageous model systems for the study of photosynthesis and other molecular, biochemical, and cellular-level phenomena of wider importance. Examples include Melvin Clavin’s explanation of light-independent (“dark”) reactions of photosynthesis in the green alga Chlorella. Studies of algae have been essential to our understanding of basic photosynthetic processes, and they continue to break new conceptual ground.

5.6 Variations in algal nutrition The old concept of algae as a simple phototrophic group has now to be modified. Photoautotrophy, they synthesis of the essential metabolites from simple chemicals and light energy, is however, still a feature of many algae (e.g. many Chlorophyta, diatoms and Cyanobacteria) and is obligate. Carbon fixation is important event for autotrophic species, that the transformation of dissolved inorganic carbon, such as carbon dioxide or bicarbonate ion, into an organic form. Photosynthesis is also a kind of carbon fixation:

6CO2 + 12H2O ————→ C6H12O6 + 6O2 + 6H2O Carbon dioxide

Water Light energy

Chlorophyll

Glucose Oxygen Water

The majority of algal groups contain heterotrophic species that obtain organic carbon from the external environment either by ingesting particles by a ingesting particles by a process known as phagotrophy, or through uptake of dissolved organic compounds, an ability termed osmotrophy. Some algae, referred to as auxotrophs, are incapable of synthesizing certain essential vitamins and hence must import them. Only there vitamins are known to be required by auxotrophic algae—biotin (vitamin H), thiamine (B1), and cobalamin (B12).

Numerous algae exhibit a mixed mode of nutrition; that is, photosynthesis in addition to osmotrophy and/or phagotrophy—an ability termed mixotrophy. Mixotrophic organisms (e.g. Euglena spp.) have a tendency to metabolize photographically in the light and heterotrophically in the dark; these may be termed amphitrophic. Some algae (e.g. Ochromonas sp.) possess pigments in such small amount that although they can photosynthesize this alone is not sufficient for growth. Another example of mixotrophy in a nonflagellate alga is the uptake of dissolved amino acids by rhizoids of the green seaweed Caulerpa.

In addition to inorganic and organic components, phototrophic algae require an external source of energy. This energy is provided by light of wavelengths between 400 and 700 nm and it is absorbed by the photosynthetic pigments located, usually, but not always, in distinct plastids.

General nutrition types: Photoautotrophy: Organisms that obtains its organic nutrients by means of photosynthesis: obligate photoautotrophs are restricted to this form of nutrition (Photoautotrophic).

Chemoautotrophy: Organisms using inorganic sources of carbon, nitrogen, etc., as starting material of biosynthesis, and an inorganic chemical energy source (Chemoautotrophic).

Photoheterotrophy: A form of nutrition in which light is captured and used as an energy source by a pigmented alga, which, at the same time, takes up dissolved organic compounds from the environments (Photoheterotrophic) (e.g. Chrycochromulina sp., a marine and freshwater Haptophyta)

Chemoheterotrophy = Chemotrophy: Organism obtaining energy by taking in and oxidizing chemical components by the breakdown of complex organic pounds (food).

Mixotrophy: A form of nutrition in which both autotrophy and heterotrophy may be utilized, depending on the availability of resources.

Auxotrophy: The nutritional requirement for one or more vitamins (auxotrophic).

5.7 Summaries of the nine algal phyla Phylum Cyanobacteria (Cyanophyta, blue-green algae).

This phylum is a well-defined group of eubacteria. Cyanobacteria include unicellular and filamentous forms, some having specialized cells. Uniquely among bacteria, cyanobacteria produce oxygen as a product of photosynthesis. Chlorophyll a and accessory and protective pigments (phycobilins and carotenoids) are present, associated with membranous thylakoids. Some members of the group (prochlorophytes) also possess chlorophyll b. The photosynthetic storage products include an α-1,4-glucan known as cyanophytan starch. Among autotrophs, cyanobacterial cells are unique in being prokaryotic in organization, hence typical eukaryotic flagella and organelles (chloroplasts. mitochondria and nuclei) are lacking. Cyanobacteria are common and diverse both freshwater and the sea. Sexual reproduction of the typical eukaryotic type, involving gamete fusion, is not present.

Phylum Glaucophyta Glaucophytes includes several eukaryotes having blue-green plastids (known as

cyanelles or cyanellae) that differ from other plastids and resemble cyanobacteria in several ways including the possession of a thin peptidoglycan wall. The cyanelles/plastids possess chlorophyll a and phycobilins, as well as carotenoids. Granules of true starch (an α-1,4-glucan are produced in the cytoplasm. There are about nine genera, all freshwater. Sexual reproduction is unknown. This group has sometimes been included within the red algae.

Phylum Euglenophyta This phylum contains euglenoid flagellates, which occur as unicells or colonies. There

are about 40 genera, two thirds of which are heterotrophic, some having colorless plastids and some lacking plastids altogether. One third have green plastids with chlorophyll a and the accessory pigment chlorophyll b as well as the carotenoids that are typical of green algae, and are capable of photosynthesis. Cell walls are lacking, but there is a protein-rich pellicle beneath the cell membrane. One to several flagella may be present, and non flagellate cells can undergo a type of motion involving changes in cell shape. The storage material is not starch but rather a β-1,3,-linked glucan known as paramylon, which occurs as granules in the cytoplasm of pigmented as well as most colorless forms. Most of the 900 or so species are freshwater, and sexual reproduction is not known.

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Phylum Cryptophyta Cryptophyta contains the unicellular cryptomonad flagellates, with 12-13 genera. A

few are colorless, but most possess various colored plastids with chlorophyll a. Chlorophyll c, carotenoids, and phycobilins constitute the accessory pigments. Alloxanthin is a xantophyll that is unique to cryptomonads. There is not a typical cell wall. Rather, rigid proteinaceous plates of various shapes occur beneath the cell membrane. Cells can be recognized by their typical flattened asymmetrical shape and the two anterior, slightly unequal flagella. The storage carbohydrate is starch, located in a space between plastid membranes. There are about 100 freshwater species and about 100 marine species. There is some evidence for sexual reproduction.

Phylum Haptophyta Haptophytes comprises unicellular flagellates or nonflagellate unicells or colonies that

have flagellate life-history stages. The photosynthetic pigments include chlorophyll a, and accessory and photoprotective pigments including chlorophyll c and caretonoids such as fucoxanthin. Species vary in the form of chlorophyll c and presence of absence and form of fucoxanthin. There is a β-1,3-glucan storage material. Two flagella and nearby sturctire known as a haptonema characterize the apices of flagellates. Many species, known as coccolithophorids, produce calcium carbonate-rich scales called coccoliths. The 300 species are primarily marine. Sexual reproduction, known in some cases to involve heteromorphic alteration of generations, is widespread.

Phylum Dinophyta This phylum includes the dinoflagellates, mostly unicellular flagellates having two

dissimilar flagella. About one half of the 550 genera are colorless heterotrophs; the rest possess plastids that vary significantly in pigment composition and type of Rubisco, the enzyme responsible for photosynthetic carbon fixation. Pigmentation is usually golden-brown, reflecting the common occurrence of the unique accessory xanthophyll peridinin, but green and other colors are known. True starch granules occur in the cytoplasm. The cell covering is a peripheral layer of membrane-bound vesicles, which in many cases enclose cellulosic plates. Of the 2000-4000 species, the vast majority are marine; only about 220freshwater forms are recognized. Symbiotic dinoflagellates known as zooxanthellae occur in reef-forming corals and other marine invertebrates. Sexual production is known.

Phylum Ochrophyta This phylum includes diatoms, chrysophyceans, phaeophyceans (brown algae), and

some other groups. Members range in size from microscopic unicells to giant kelps (60 m in length) having considerable tissue differentiation. Chlorophyll a is present in most ochrophytes, but some colorless heterotrophic forms also occur. I the pigmented forms, dominant accessory and photoprotective pigments may include chlorophyll c and carotenoids such as fucoxanthin or vaucherianxanthin. The food reserve is cytoplasmic lipid droplets and/or a soluble carbohydrate (β-1,3-glucan chrysolaminaran or laminaran) which occurs in cytoplasmic vacuoles. There are usually two heteromorphic flagella, one bearing many distinctive three-piece hairs known as mastigonemes. Cell coverings vary widely and include silica scales and enclosures as well as cellulose cell walls. There are more than 250genera and 10.000 species of extant diatoms alone. Some groups of the Ochrophyta are primarily freshwater, some are primarily marine, and some, such diatoms, are common in both fresh and salt water. The brown algae known as the giant kelps are the largest of all the algae. Sexual reproduction is common, and several types of life cycles occur.

Phylum Rhodophyta (Red algae) Red algae have members that occur as unicells, simple filaments, or complex

filamentous aggregations. Pigments are present in all except certain parasitic forms, and include chlorophyll a together with accessory phycobilins and carotenoids. Flagella are not present. The cytoplasmic carbohydrate food reserve is granular Floridian starch, an α-1,4-glucan. Cell walls are loosely constructed of cellulose and sulfated polygalactans, and some are impregnated with calcium carbonate. The calcified red algae known as corallines are widespread and ecologically significant in coral reef systems. The 4000-6000 species are primarly marine, favoring warm tropical waters. Sexual reproduction is common, as is alteration of generations. A triphasic life history characterizes most red algae and is unique to this group.

Phylum Chlorophyta (Green algae) Green algae have unicellular or multicellular thalli. Some are flagellates, and others

produce reproductive cells, the majority of which are biflagellate. In addition to chlorophyll a, the pigments chlorophyll b, β-carotene, and other carotenoids occur in plastids. Uniquely, starch is produced within plastids of green algae (and land plants).Cell walls of some are cellulosic as in land plants, but the walls of other green algae are composed of different polymer, and some are calcified. Early divergent flagellates and one multicellular clade (the ulvophycean green seaweeds) are primarily marine, whereas other groups are primarily terrestrial or freshwater. One of the freshwater lineages (the charophyceans) gave rise to the land plants (embryophytes). There are about 17,000 species. Sexual reproduction is common, and all three major types of life cycle occur.

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6 GENERAL FEATURES OF ALGAL DIVISIONS 6.1 Division CYANOBACTERIA (Blue-green algae) Cyanobacteria, also known as chloroxybacteria, blue-green algae, or Cyanophyta, are significant for many reasons. Cyanobacteria were the dominant forms of life on earth for more than 1.9 billion years. They were the most ancient oxygen-producing photo synthesizers; the first to produce chlorophylls a and b as well as a variety of accessory photosynthetic pigments; producer of massive carbonate formations in shallow waters during the Precambrian period; and the earliest (Precambrian) terrestrial autotorophs. The chloroplasts of eukaryotic algae and plants are descended from Cyanobacteria.

The oldest fossils attributed to cyanobacteria are 3.5 billion-year-old remains from the Apex Basalt, a geological deposit in western Australia. Stromatolite is the fossilized remains of a colony or mat of bacteria cyanobacteria that normally exhibits either a domed or a column-like shape, and the sediment in which it lies may be marked with fine concentric bands (Figure 6.1). The layers were produced as calcium carbonate precipitated over the growing mat of bacterial filaments; photosynthesis in the bacteria depleted carbon dioxide in the surrounding water, initiating the precipitation. The minerals, along with grains of sediment precipitating from the water, were then trapped within the sticky layer of mucilage that surrounds the bacterial colonies, which then continued to grow upwards through the sediment to form a new layer.

Figure 6.1 A stromatolite that has been split open, revealing the layering typical of these formations

Cyanobacteria contain chlorophyll a, which differs from the chlorophyll of those bacteria, which are photosynthetic, and also free oxygen is liberated in blue-green algal photosynthesis but not in that of bacteria.

The origins of the blue-green algae are unclear. It is attempting to assign them to an evolutionary path parallel to that of the photosynthetic bacteria, but as the group that evolved the pathway for evolution of oxygen. No transition forms between these two types of photosynthesis have been found, however, and thus there are no likely candidates for the ancestral of the blue-green algae.

6.1.1 Habitat Blue green algae are very common in waters of a great range of salinity and temperature, and they occur in and on the soil and also on rocks and in their fissures. Little recorded the occurrence of Gleocapsa, Nostoc in the supralittoral zone of marine shores. A number have been recovered from the atmosphere. In general blue-green algae seem to be more abundant in neutral or slightly alkaline habitats, although some (Chroococcus) are said to be to occur in bog waters at pH 4. Blue-green algae are absent from waters whose pH was less than 4 or 5, while certain eukaryotic algae are present. Blue-green algae are both planktonic and benthic. Some planktonic forms for example, Microsystis aeruginosa, Anabaena flos-aquae, Trichodesmium erythraeum. The last species common in tropical waters, including the Red Sea (which probably was so named because of the colour of the alga). At least two blue-green algae, Microcystis aeruginosa and Anabaena flos-aquae, are responsible for acute poisonings of various animals.

Blue-green algae, along with certain bacteria, occur in alkaline hot springs, they can live at maximum temperatures of 73-74ºC. Some Cyanobacteria of soil have been shown to remain viable for 107 years and they have been recovered from house dusts.

A number of blue green algae grow in association with other organisms. Gleopacsa and Nostoc are the phycobionts of lichens, while others like Nostoc and/or Anabaena occur within the plant bodies of certain liverworts, water ferns, cycads and angiosperms where they can fix nitrogen. Certain types are associated with Protozoa, where they have been called cyanelles.

In addition to poisoning animals, blue-green algae may be deleterious to human beings. For example Lyngbya majuscula causes dermatitis.

6.1.2 Nitrogen Fixation Cyanobacteria are the only algae known to be capable of transforming molecular nitrogen gas into ammonia, which has can then be assimilated into amino acids, proteins, and other nitrogen-containing cellular constituents. Three kinds of blue-green algae have been shown to fix nitrogen: 1- the filamentous heterocystous species 2- certain unicellular (nonheterocystous filamentous species, 3- certain nonheterocystous filamentous species, Plectonema boryanum, although only under microaerophilic conditions. The nitrogen-fixing enzyme complex nitrogenase is oxygen-sensitive, so that the highest rate of nitrogen fixation occurs under reduced oxygen tensions. There is evidence that heterocysts reduce the elemental nitrogen and transfer it to the adjacent vegetative cells. Experiment shows that Phycocyanin which is a nitrogen reserve, declines in nitrogen-starved cultures. Under aerobic conditions, phycocyanin developed in the vegetative cells next to the heterocycts. It reappears, under anaerobic conditions, in the all the vegetative cells. Experiments show the sensitivity of nitrogenase to oxygen and indicate that less oxygen apparently is present in the heterocysts than in the vegetative cells.

It has been hypothesized that the sheaths of Gleocapsa, a unicellular blue-green alga that fixes nitrogen, may somehow affect microaerophilic conditions in the cells that permit nitrogenase activity.

The nitrogen-fixing capacity of blue-green algae has been made use of in the cultivation of rice in which their growth is encouraged in the rice paddies.

6.1.3 Protoplast The photosynthetic lamellae or thylakoids of blue-green algae, unlike those of other chlorophyllose plants, are not enclosed in membrane-bounded groups to form chloroplasts. Instead, they lie free in the cytoplasm. The thylakoids are the site of chlorophyll a, and the

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accessory pigments also occur on their surfaces in the form of small particles, the phycobilisomes. The accessory pigments are c-phycocyanin, c-allophycacyanin, and c-phycoertytrin, the two former blue and the latter red.

Photosynthetic storage product of cyanobacteria is cyanophycean starch = cyanophycin (also known as cyanophytan starch or glycogen).

Figure 6.2 Heterocysts (arrows) in Anabaena, illustrating some

of the variation in heterocycsts appearance that occurs among taxa. Note the conspicuous mucilaginous sheath (arrowhead)

Figure 6.3 An akinete (arrowhead) in Anabaena.

6.1.4 Motility Many filamentous blue-green algae are not enclosed in firm sheaths; the hormogonia of those that are, and some unicellular species, undergo movement when in contact with the substrate. This movement, accomplished without evident organs of locomotion, is called gliding movement and occurs also in some filamentous bacteria. It is thought that the oscillation of certain trichomes like those of species of Oscillatoria is related to these waves of propulsion of the superficial fibrils.

6.1.5 Form The cyanobacteria contain unicellular, colonial, and filamentous species. A filament is composed of a chain of cells, the trichome, and the enveloping stealth, if one is present. The term trichome (meaning “hair”) is used as a synonym for an unsheathed individual filament. The term hormogonium is applied to a short filament that results from break up of longer filaments and serves as a means of vegetative reproduction.

6.1.6 Reproduction The biological species concept cannot be used with cyanobacteria because sexual fusion of gametes completely absent from these prokaryotes. In the unicellular blue-green algae, reproduction is effected by cell division. In cell division in most blue-green algae, the cell

becomes constricted in the median plane and the two inner wall layers grow centripetally until a septum is formed.

Colonial and filamentous Cyanobacteria reproduce by fragmentation in which segments of the organism become separated from the parent, glide or float away, and grow into new individuals. Fragmented sections of trichomes, called hormogonia are motile. They arise by separation of adjacent terminal walls in the trichome or by the death of certain cells that may become biconcave separation discs or necridia.

6.1.7 Akinetes The specialized cells known as akinetes are thought to function as resting cells that allow cyanobacteria to survive adverse conditions. Akinetes are produced only by cyanobacteria that are also capable of producing heterocysts. These two types of specialized cells share a number of features that distinguish them from vegetative cells. Particular glycolipids and polysaccharides occur in the cell walls of both heterocysts and akinetes, but not vegetative cells. Also, photosystem II is inactivated in the akinetes of at least some cyanobacteria, as it typically the case for heterocysts. The observations suggest that early stages in the differentiation of akinetes and heterocysts may be under the control of similar genetic elements. Akinetes are typically distinguished from heterocysts, however, by absence of specializations associated with nitrogen-fixation and, often, by large size. In many cases the akinete wall is distinctively ornamented and may be darkly pigmented.

An akinete develops from a vegetative cell that becomes enlarged and filled with food reserves (cyanophycin and glycogen granules) and increases its wall externally by an additional complex investment. After a period of dormancy, the akinete may germinate.

a

b

Figure 6.4 Tolypothrix. (a) Hormogonia. (b) Separation disk (arrowhead) adjacent to a heterocyst; this is where false branches

usually occur in this organism.

Some viruses attack blue-green algae; these have been designated phycoviruses or blue-green algal viruses (BGA viruses). The virus lyses and destroys the host algal cells. There is some evidence from filed and laboratory tests that phycoviruses like LPP-1 may be effective in controlling unwanted blooms of blue-green algae in nature.

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6.1.8 Cyanobacteria and the origin of an oxygen-rich atmosphere It is though that at the time when cyanobacteria first appeared (3.5 billion years ago), the earths atmosphere was rich in carbon dioxide (10-100 times present level) and that oxygen was sparse (about 10-8 times that of present levels). Cyanobacterial photosynthesis would not have been limited by the availability of carbon dioxide, but oxygen-requiring eukaryotes would not have been to exist. Thus the cyanobacteria dominated earth’s biosphere for at least one billion years and probably more. Oxygen derived from their photosynthesis gradually accumulated in the atmosphere, eventually reaching modern levels, about 21%. The rise to dominance of cyanobacteria—the earliest known oxygenic photosynthesizers—has been described as the single most significant evolutionary event in the history of life on earth, for without it, subsequent origin of eukaryotic life would have been impossible.

An oxygen-rich atmosphere made aerobic (oxygen-using) respiration possible. The use of oxygen as an electron acceptor resulted in an 18-fold increase in respiration efficiency, necessary for survival of most eukaryotes. An oxygen-rich atmosphere—poisonous to all anaerobic (non-oxygen using) prokaryotes—also caused a radical change in community dominance by favouring organisms possessing aerobic metabolism. Finally, an oxygen-rich atmosphere was necessary for generation of the stratospheric ozone shield that protects life on earth’s surface from the damaging effects of ultraviolet radiation. This allowed algae and other organisms to colonize surface waters and the land surface, habitats previously rendered sterile by UV.

eukaryotic cells

Multicellular forms 0

600

1000

autotrophs (photosynthesis)

prokaryotic cells

Cenozoic

organic evolution

chemical evolution

formation of Earth 5000 mya

Mesozoic

Paleozoic

Precambrian

Oxy

gen

from

pho

tosy

nthe

sis

Oxy

gen

accu

mul

ates

in a

tmos

pher

e free oxygen

heterotrophs

Figure 6.5 Diagram illustrating that atmospheric oxygen increase is correlated with the appearance and radiation of eukaryotes.

(mya=millions of years ago)

6.2 Division EUGLENOPHYTA The name of Euglenophyta comes from genus Euglena which means; eu, good, true, in Greek + glene, eye, in Greek.

Euglenoids are generally found in environment where there is an abundance of decaying matter. Such habitats may also include nearshore marine or brackish sand and mud flats characterized by decaying seaweeds or organic contamination, farm ponds, dipteran larvae hindguts, and the rectum of tadpoles. Sometimes euglenoids form alarming blood-red surface blooms that, so far as is known, are not harmful. However, in nearshore marine waters large populations of euglenoids have been observed to occur among blooms of potentially toxic algal species.

Because of their association with increased level of dissolved organics, euglenoids have been used as environmental indicators of such conditions.

Mobile cells usually have only a thin mucilage layer, while immobile cells lacking flagella may be embedded in relatively thick layers of jelly to form scum on water or other surfaces that is one cell layer thick. Such mucilage-embedded immobile stages of cells––that under other conditions are mobile––occur in a number of algal groups and are known as palmella or palmelloid stages (Figure 6.8)

Except when they are encysted or in a palmella phase, Euglenoids are flagellate, having two or several flagella. When there are two, one may be nonemergent from the anterior invagination which consists of a canal and a reservoir. Euglenoid flagella are rather coarse as compared with those of Chlorophyta. They have the usual (9+2) fibrillar arrangement and in addition a paraflagellar rod.

The cell covering of euglenoids is known as pellicle. The euglenoids are probably the earliest divergent (most ancient) group of eukaryotic algae. Only about one third of the known genera possess green-pigmented chloroplasts. A number of euglenoid genera are phagotrophic (i.e. they feed upon organic particles) and consequently possess cellular organelles that are specialised for capture and ingestion of prey, including bacteria and small algal cells. Some euglenoid predators are indiscriminate feeders, while others specialize, feeding only upon selected diatom, for instance.

Ultrastructural surveys of cell structure and mitosis of euglenoids revealed close relationship to a group of flagellate protozoa known as the kinetoplastids. Subsequent molecular analysis corroborated this relationship and strongly suggested that a kinetoplastid/euglenoid clade originated quite early within eukaryotes. The kinetoplastids are a great important group because they include parasitic trypanasomes. Leismania tropica causes Aleppo boil (Şark çıbanı, halep çıbanı). They contaminate to human with an insect as a porter. Trypanasome gambiense cause sleeping sickness in Africa. T. cruzi cause Chagas sickness in Latin America.

Euglenoids are distinguished from kinetoplastids by two principal features. The first is the producing reserve storage granules known as paramylon, that does not stain blue-black iodine-iodide solution and is found in the cytoplasm of even colourless form. The second distinguishing feature is a superficial pellicle composed of ribbon-like, interlocking proteinaceous strips that wind helically around cells just beneath the plasma membrane, giving cells are striated appearance.

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6.2.1 Reproduction Sexual reproduction does not occur in euglenoids with regularity, if at all. Asexual reproduction is by longitudinal division, proceeding from apex to base, such that euglenoids in the process of cytokinesis appear to be “two-headed”

In response to changing environmental conditions, euglenoids may form resting cysts. Cyts formation involves loss of flagella, increase in the number of paramylon granules, swelling and rounding of the cells, increase in the number of mucilage bodies.

Figure 6.6 Diagram illustrating typical features of Euglena, which include the flask-shaped pocket (reservoir), from which one of the two flagella emerges. Adjacent the reservoir are the eyespot and contractile vacuole. Also typically visible with the light microscope are paramylon granules, plastids, and the nucleus with nucleolus and relatively large chromosomes. (b) TEM view of longitudinally sectioned Euglena cell. Note eyespot (ES), plastids (P) with pyrenoids (Py) and Nucleus (N).

Figure 6.7 Dividing Euglena cell with characteristic two-headed appearance. Note also the large number of paramylon granules.

Figure 6.8 This is the palmelloid stage of development where the Euglena rounds up into a ball discarding its flagellum. They will stay in this stage until their environment improves.

6.2.2 Euglenoid ecology There are no truly planktonic euglenoid species. They are fundamentally occupants of interfaces, such as the air-water and sediment-water boundaries. In such habitats euglenoids can be infected by chytrids (primitive fungi) and consumed by herbivores including other euglenoids, such as predacious Peranema. The euglenoid storage product, paramylon, is comparatively indigestible; paramylon granules have been observed to pass through the gut of herbivores unharmed. In order to digest euglenoid storage products, herbivores require a gut enzyme, laminarase that can degrade paramylon.

Certain euglenoids are known for tolerating extreme conditions. Some seem able to migrate into soils and persist there for long periods in a dormant state. Euglena mutabilis is able to grow in extremely low pH waters, such as streams draining coal mines and the acidic, metal contaminated ponds. The optimal pH for growth of this species is 3.0 but pH values lower than 1.0 can be tolerated. Euglenoids are also reported to be able to adapt to salinity increases more quickly than can other algae.

6.3 Division CRYPTOPHYTA Cryptomonads, their name literally meaning “hidden single cells”, are among the most inconspicuous of the algae. Cryptomonads are relatively small 3-50 µm in length––members of the phytoplankton; they are often most abundant in cold or deep waters; they are readily eaten by a wide variety of planktonic herbivores; and natural collections are not easily preserved. The cell tending to burst readily when subjected to environmental shock. Cryptomonads are probably most appreciated by plankton ecologists who recognize their high quality as food for zooplankton and algal evolutionary biologists who not that significant cryptomonads ultrastructure and molecular biology in the study of secondary endosymbiosis.

Cryptomonads and euglenoids share a number of characteristics.

Sharing features of the euglenoids and cryptomonads;

1. They occur fresh and marine environment

2. B vitamin is required by all members of both groups.

3. Fundamentally biflagellate, with flagella emerging from an apical depression.

4. They are primarily unicells that can also occur as nonmotile, mucilage embedded palmelloid stages and most forms of both groups are essentially naked.

5. They can produce thick-walled cysts that are able to survive adverse conditions, but neither group has a good fossil record.

6. Plastids of both groups arose by secondary endosymbiosis.

7. Photosynthetic storage of both groups occurs as granules in the cytoplasm.

Such similarities do not indicate that cryptomonads and euglenoids are closely related. Strong ultrastructural and molecular evidence links the cryptomonads with the Glaucophytes.

Photosynthetic storage material in cryptomonads is starch, which like that of plants and green algae, (but unlike euglenoid paramylon), stains blue-black with an iodide-iodid solution.

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a

b Figure (a) Cryptomonas obovata (b) Cryptomonas ovata

6.3.1 Ecology Cryptomonads are especially prominent in oligotrophic, temperate, and high-latitude waters of lakes and oceans. They seem to be more important in cold waters both lakes and oceans. They seem to be more important in cold waters, typically becoming abundant in winter and early spring when they can begin growth under the ice. For example, cryptomonads may dominate the spring phytoplankton bloom in the North Sea where they are believed to make significant contributions to net primary productivity. Localized blooms of cryptomonads also occur in Antarctic waters; the bloom is correlated with the influx of water from melting glaciers. In perennially ice-covered Antarctic lakes, Chroomonas lacustris or a Cryptomonas species may dominate the algal flora during the austral summer, contributing more than 70% of the total phytoplankton biomass. Crytomonads seem to occur only rarely in ocean waters at temperatures of 22ºC or higher, and they are absent from hot spring and hypersaline waters.

In oligtrophic freshwater lakes, cryptomonads typically form large populations in deep waters (15-23 m) at the junction of surface oxic (oxygen-rich) and bottom anoxic (oxygen-poor) zones, where light levels are much lower than in surface waters.

A significant ecological aspect of cryptomonads is their incorporation within cells of the mixotrophic ciliate Myrionecta rubra. This protozoan can form dramatic, red colored blooms in waters off the coast of Peru and Baja, typically upwelling conditions that bring additional nutrients to surface waters. The photosynthetic pigments of the cryptomonad endosymbionts impart a red coloration to the ciliate host.

Certain dinoflagellates, including Gymnodinium acidotum and Amphidinium wigrense, also regularly contain portions of cryptomonad cells, particularly plastids. These dinoflagellates possess phagotrophic capabilities and can thus harvest most or parts of crytomonads or other cells. In some cases the cryptomonads possess nuclei, but in others, only the plastids persist within the dinoflagellate cytoplasm.

Figure 6.9 Cross section through an unidentified cryptomonad, viewed with TEM. Note the peripheral plastid (P), pyrenoid (Py) and starch (S), Golgi body (G).

6.4 Division HAPTOPHYTA Haptophyta algae are primarily marine unicellular biflagellates that have had a major impact on global biochemistry for at least 150 million years. They are probably the single modern algal group that has the greatest long-term impact on carbon and sulfur cycling and hence, global climate. Most haptophyta species produce external body scales composed primarily calcium carbonate that are known as coccoliths. Sedimented coccoliths are the major contributors to ocean floor limestone accumulation, and represent the largest long-term sink of inorganic carbon on the earth. Deep-sea carbonate deposits cover about one half of the world’s seafloor, an area that represents one third of the earth’s surface. Coccoliths contribute about 25% of the total annual vertical transport of the deep ocean. In addition, the coccoliths-producing Emiliana huxleyi, are known for their formation of extensive ocean blooms with concomitant production of large amounts of dimetylsulfide (DMS), a volatile sulfur-containing molecule that increases acid rain. Coccoliths, which readily reflect light, and DMS, which enhances cloud formation, contribute to increased albedo (reflectance of the earth’s surface) and thus have a cooling influence on the climate.

Haptophyta are also important in terms of their biotic associations. Most haptophytes contain golden or brown plastids, and are thus photosynthetic primary producers. However, many are osmotrophic or phagotrophic; thus mixotrophy is common. Phagotrophy is particularly prominent among forms that lack a cell covering formed of coccoliths, but which possess a haptonema, a thread-like extension from the cell that is involved in prey capture, among other functions. A haptonema occurs in many haptophytes, hence the name of the group, although a number of taxa appear to have lost this structure.

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climate

albedo latent head

storms

DMS

nutrients

CO2

temperature

clouds

carbonate

CO2

organic carbon

acid rain

sediments

respiration

Emiliania

Figure 6.10 Blooms of Emiliana huxleyi can have important effects on the earth’s climate in a variety of ways, summarized here

in diagram form.

Chrysochromulina polylepis can produce toxic offshore marine blooms that cause death of fish and invertebrates, while Prymnesium parvum causes similarly toxic blooms in brackish waters. In 1989, a P. parvum bloom along the Norwegian coast caused a five-million-dollar loss of salmon.

With the exception of the toxic bloom-formers, haptophyta algae, because of their small size, fast growth rates, digestibility, and nutritional content, are considered to be high-quality foods for marine zooplankton. Haptophyta actually reach their highest species diversity in extremely low-nutrient, subtropical open-ocean waters, where a number of strange and beautiful forms mysteriously occur in nearly dark ocean waters more than 200 m deep.

6.4.1 Fossil record The haptophyte algae have one of the best fossil records among the algae, because of often round or oval calcite coccoliths are readily preserved in sediments. Coccoliths (Gr. kokkos, berry + lithos, rock) were named in 857 by T. H. Huxley, who observed them in samples of deep-ocean sediments. Coccoliths first appear in the fossil record either as early as carboniferous, or in the Late Triassic (about 220 million years ago), continuing to the present time.

CaCO3

CO2

CO2

CO2

HCO3-

Ca2+

CO2

coccolith

Figure 6.11 A diagram of an Emiliania huxleyi cell, illustrating that bicarbonate is taken into the cell and used in calcification,

which then provides additional CO2 for photosynthesis.

The rise of coccolithophorids followed the most dramatic worldwide extinction episode in earth’s history—the 250million year ago end-Permian event. A richly diverse marine community experienced the loss of 85% of its species. The cause is though to have been extensive volcanism with the release of large amounts of CO2, resulting in acid rain, and cooling caused by atmospheric ash, though other causes are also possible.

The abundance of coccolith fossils peaked during the Late Cretaceous (63-95 million years ago), when very extensive chalk deposits were laid down across much of northern Europe and other sites around the world. In fact, the term Cretaceous refers to this chalk. Some blackboard chalks that are derived from such deposits contain coccolith remains.

The impact of massive asteroid or comet off the Yucatan coast (the famous “K/T event”), which is associated the demise of dinosaurs and ammonites, also apparently caused extinction of 80% of the coccolithophorids species that had been present in the cretaceous. In contrast, dinoflagellates and diatoms seem to have escaped similar drastic extinction effects.

Because coccolith are common, small, and exhibit low endemism (restriction of certain species to particular locales), they are widely used as stratigraphic indicators to match rocks of equivalent ages from different locales. About 1000 species of fossil coccolithophorids are widely used as bioindicators in the oil industry.

6.4.2 Thallus type The most primitive haptophytes are thought to be biflagellate unicells having a haptonema. Derived forms are considered to include flagellates with a highly reduced haptonema or none at all, as well as nonflagellate amoeboid, coccoid, palmelloid, colonial, or filamentous forms that produce biflagellate reproductive cells. Coccolith production is regarded as a derived feature. Thus haptophytes probably originated much earlier than is suggested by the first appearance of coccoliths in the fossil record, but did not leave remains because earliest forms lacked distinctive fossilizable parts.

The haptonema, if present, emerges from the cell apex, between the flagella. The haptonema is about the same thickness as a flagellum and was mistaken for a flagellum until its structure was elucidated with transmission electron microscopy. The length and bending behavior of

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the haptonema seem to be correlated with phagotrophic behavior; species having a very long haptonema are inclined toward phagotrophy, whereas those having a very short or no haptonema are not.

(a) (b) (c) (d)

Figure 6.12 A diagram of the feeding process of Chrysochromulina. In (a) and (b), particles adhere to the haptonema and are

translocated downward to a particle aggregating center. In (c), the aggregated, captured particles are moved to the tepi of the haptonema. In (d), the aggregate is delivered to the cell surface (at the posterior end of the cell) through bending of the haptonema. Here is taken into the cell.

High speed video methods revealed of the haptonema in phagotrophy. As the cell swims forward, prey particles—such as bacterial cells—attach to the forward-projecting haptonema. Edhesive properties are attributed to presence of sugar groups at the haptonemal surface. Particles are moved downward to a point about 2 µm distal to the haptonemal base, known as the particle aggregating center (PAC). Once formed, the PAC moves up to the haptonemal tip

6.5 Division DINOPHYTA (dinoflagellates) Dinoflagellates probably rank first among the eukaryotic algae in terms of the current and potential future significance of their biotic association, which may have large impacts on carbon cycling and coastal fisheries production. Dinoflagellate endosymbionts are essential to the formation and existence of coral reef ecosystems; they exhibit an amazing diversity of nutritional types, including autotrophs, mixotrophs, phagotrophs, and parasites; and some are notorious for the production of toxic red tides (harmful algal blooms). These species reproduce in such great numbers that the water may appear golden or red, producing a "red tide". When this happens many kinds of marine life suffer, for the dinoflagellates produce a neurotoxin which affects muscle function in susceptible organisms. Humans may also be affected by eating fish or shellfish containing the toxins. The resulting diseases include ciguatera (from eating affected fish) and paralytic shellfish poisoning, or PSP (from eating affected shellfish, such as clams, mussels, and oysters); they can be serious but are not usually fatal.

The term dinoflagellate originates from the Greek word dineo, meaning “to whirl”. However, there are several non flagellate amoeboid, coccoid, palmelloid, or filamentous forms.

Dinoflagellates are second only to diatoms as eukaryotic primary producers in coastal marine waters. Though most of too large (2-200 µm) to be consumed by filter feeders, dinoflagellates

are readily eaten by large protozoa, rotifers, and planktivorous fish, for which they can be (if not toxic) high-quality food.

They exhibit high levels of living and fossil biodiversity (more than 550 genera and 4000 species); and the internal complexity of their cells rivals that of ciliate and sarcodine protozoa.

Together with cell membrane, the dinoflagellates cell covering consists of a single layer of several to many closely adjacent, flattened amphiesmal (thecal) vesicles; the entire array is known as the amphiesma. In many species the thecal vesicles each contain a thecal plate composed of cellulose; such species are said to be armored or thecate. In some species the ampiesmal vesicles are not good developed, cells appear to be naked and are referred to as unarmored or non-thecate. Soma dinoflagellates dinospores of the invertebrate symbiont (Symbiodinium) are regarded as intermediate between the armored and unarmored condition.

About half of the known species lack plastids and are there fore obligatory heterotropnic. Parasitic forms also occur within the cells or tissue of fish, invertebrates, and filamentous algae.

a b

Figure 6.13 Armored dinoflagellates (a) Ceratium hirudinella (b) Peridinium

6.5.1 Bioluminescence There is evidence that the bioluminescence exhibited by marine dinoflagellates has a defensive function. When the algal cell agitated, they produce blue-green light that results from reaction of the substrate luciferin with the enzyme luciferase, as in fireflies and various bacteria. In the case of dinoflagellates, bioluminescence appears to decrease copepod predation. Two possible protective mechanisms have been suggested: a direct “startle” effect on the herbivores themselves and a more indirect effect—increased predation upon copepods that have fed upon glowing dinoflagellates and thus rendered more visible to their predators.

Bioluminescence occurs in approximately 30 photosynthetic dinoflagellates, including Gonyaulax and some non-photosynthetic marine forms, such as Noctiluca (Figure 6.14)

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luciferin

luciferase + O2

oxiluciferin

0,1-s blue light

Bioluminescent dinoflagellates possess spherical intracellular structure known as scintillons or microsources. These are about 0,5 µm in diameter and are arrayed at the cell periphery. They are derived from the Golgi apparatus and contain luciferin, luciferase oxidizes the luciferin with molecular O2, causing a 0,1-s flash of blue light.

The number of scintillons in Gonyaulax polyedra decreases from 540 per cell in the night phase to just 46 in day-phase cells, and the amount of bioluminescence is two orders at magnitude grater in night-phase cells. There is a daily (circadian) rhythm in synthesis and destruction of scintilloins, luciferin, and luciferase. This is viewed as an adaptation that conserves energy, as bioluminescence would not be visible in the day time.

Figure 6.14 Noctiluca scintillans, commonly known as the seasparkle, is bioluminescent. They cause the lighting of the sea.

6.6 Division OCHROPHYTA In the past covered in this division (Diatoms, Chrysophycea, Hhaeophycea) had been grouped with haptophyta in the division Chrysophyta. We use newer phylum concept Ochrophyta because it is defined in terms of flagellar ultrastructure and molecular data, and thus more closely reflects modern concepts of evolutionary relationships than do older taxonomic concepts. Brown seaweeds and golden-brown diatoms, as well as incredibly diverse array of other algae, belong to a group that we have chosen to call the Ochrophyta, or more informally, the ochrophytes. The name reflects the ocher (golden-brown) color of many algae in this group.

The term heterokont is using for Ochrophyta. This means “different flagella.” Although other groups of algae possess flagella that are also distinctively different from each other (dinoflagellates, for example) the organisms known as heterokonts typically have two flagella (or have reproductive cells with such flagella) that differ in unique ways: along, forward-directed flagellum bears two rows of stiff, there-parted hairs and a shorter, smooth flagellum that often (but not always) bears a basal granule that functions in light sensing.

6.6.1 Diatoms In terms of evolutionary diversification, the diatoms have been wildly successful. Though occurring only as single cells or chains of cells, with 285 genera encompassing 10,000-12,000 recognized species, diatom diversity is rivaled among the algae only by the green algae. Some experts believe that many diatom species remain to described and that diatom species may actually number in millions.

In terms of contributions to global primary productivity, diatoms are among the most important aquatic photosynthesizers. They dominate the phytoplankton of cold, nutrient-rich waters, such as upwelling areas of the oceans, and recently circulated lake waters.

Diatoms are commonly grouped into two or there major categories, primarily on the basis of frustule features that can be readily observed in living cells as well as fossils. The centric diatoms typically have discoid or cylindrical cells having radial symmetry in face of valve view. A valve is the top or bottom of silica frustule. Incontrast, valves of pinnate (referring to “feathery” patterns of ornamentation on the frustule) diatoms have more or less bilateral symmetry.

a b Figure 6.15 A comparison of (a) Pennate diatoms, typified by bilateral symmetry, with (b) centric diatoms, which have radial

symmetry.

6.7 Division CHLOROPHYTA General features of green algae

Green pigmented algae (occasionally colourless) with true pyrenoids and starch.

Form ranges from unicellular through colonial, coenobial, filamentous, thalloid to Siphonaceous.

Chromatophores one or more, often complex, but discoid in the siphanoceous genera.

Flagellate stages possessing two (four) or rarely more flagella.

Asexual reproduction via zoospores, aplanaspores, autospores, akinetes, palmelloid stages or fragmentation.

Sexual reproduction isogamous, anisogamous, or oogamous.

Mostly haploid vegetative plants and with well developed alteration of generations in some genera.

Freshwater, terrestrial and marine, but certain groups confined to one or other habitat.

Some genera symbiotic with fungi, forming lichens, and other symbiotic with animals

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6.7.1 Class: Charophycea Charophycean green algae represent the lineage that is ancestry to the land plants. The land plants are thought to have first appeared more than 470 million years ago-the age of the earliest fossils that are accepted as land plant remains. Charophyceans have been associated with the ancestry of land plants on the basis of ultrastructural, biochemical, and molecular evidence. Molecular sequence evidence established a close relationship of charophyceans to land-plant ancestry.

Charophyceans include the macroscopic charalean algae such as Chara (for which the group is named) and Nitella, which can be very common in some freshwater environment. Charophycean algae also include microspobic desmids and the well-known Spirogyra and related filamentous algae, which are referred to as zygnamataleans (named for the genus Zygnema).

Macroscopic Charophyceans have along fossil record. This record reveals that relatives of modern charaleans were the dominant form of macrophytic vegetation in freshwaters for some three hundred million years prior to the origin of flowering plants. They are much less diverse today than in some earlier time periods, modern charaleans are widespread and locally abundant.

Microscopic charophyceans such as Spirogyra are famous for their high level of species diversity there are more than 3.000 described species, with new forms continuing to be discovered.

6.7.2 Order: Charales Modern charaleans algae are important both ecologically and evolutionarily. They are closely related to the ancestry of land plants. They have a long fossil history, based primarily upon calcified reproductive structures that provide useful information about the evolutionary process and patterns of extinction.

(a) (b) Figure 6.16 (a) Chara. (b) Nitella

6.7.3 Killer algae in the Mediterranean Sea Alien or "killer" green alga (Caulerpa taxifolia) has made its way to San Diego and Orange County. A strain of this species has invaded the Mediterranean and has spread uncontrollably since 1984. The algae has been referred to like "laying astro-turf across the ocean floor"—displacing everything in its path. It threatens coastal marine life, including native seagrass, invertebrates, fish, marine mammals, and sea birds.

The production of a deadly poison by species of Caulerpa, referred to as caulerpicin, has been recognized in Hawaii and in the Philippines and is known to enter into marine food chains. Since freshly collected plants of Caulerpa are eaten in salads in some areas of the Pacific, the health hazard is obvious. •The algae spreads by fragmentation, and even a small piece can form a new plant. It is believed the algae are transported to different areas via boat anchors and fishing gear. •It is capable of extremely rapid growth—about an inch a day. •The algae can survive in various depths and temperatures, and grows on almost any substrate; it is not free-floating.

The invasive strain of Caulerpa taxifolia was first discovered in the Mediterranean Sea in 1984. Immediate eradication was not attempted and, as a consequence, within a few years government officials determined the infestation to be uncontrollable. Today, marine scientists in the Mediterranean are largely resigned to monitoring the seaweed's continuous expansion over thousands of acres of sea floor.

The invasion of Caulerpa taxifolia: Since its introduction of the Mediterranean Sea, this anthropogene hybrid seaweed keeps still expanding at a rapid pace. From the main site of colonization (Menton to Cap d'Ail) it spreaded westwards to the municipality of Eze-sur-Mer (both sites of southern France) and even further. Here, the total affected area (places where more than 100 colonies per hectare have developed) now represents about 1360 hectare in shallow waters.

Invasive Capacity of Caulerpa taxifolia Chronology of the spread in the Mediterranean: Med Waves Report, Spring 1997

Date # of Sites in Hectares (10E3m2) Place of Location

1984 1 site at 1 m2 Monaco Coast

1990 3 sites, covering 3 hectares Same coast line

1991 30 hectares Same coast line

1993 1327 hectares French coast line

1994 427 hectares Monaco coast line

1994 1500 hectares French coast line

1995 427 hectares Same coast line

1997 4600 hectares Mediterranean Sea

1999 6000 hectares (60 km2) Mediterranean Sea

This exponential increase is not only the result of spreading over short distances through the dissemination of cuttings near the original patches.

According to last studies on the Turkey coast of Mediterranean Sea C. taxifolia was not found. But other Caulerpa species, C. rasemosa was found which not toxic like C. taxifolia. C. rasemosa is also invasive species and expanding and cover sea bottom.

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7 ECONOMIC ASPECTS Algae play a small but important part in the direct economy of many countries.

Four major products are derived commercially from algae;

1. Agar

2. Carrageen

3. Alginic acid (alginates)

4. Diatomite

The first two products are extracted from marine Rhodophyta, the third from Phaeophyceae, and the fourth from either marine or freshwater diatom deposits. Other direct uses are as food, for man and cattle, and as organic or inorganic (lime) fertilizers.

It is impossible to assess the full economic importance of algal growth but even the most conservative estimates contribute 50 per cent of global carbon fixation to the algae; in aquatic habitats algae are part of the food chain leading to crustacean and fish, on agricultural land they are an important constituent of the soil flora, and in water supply reservoirs, purification plants and in sewage disposal plants, they play an important role in oxygenation and filtration.

7.1 Agar Agar extracted from rhodophycean algae. It is used as a medium in the culture of bacteria, fungi and algae and also in numerous industrial processes. The term ‘agar’ has been used in various implications; originally the Malayan word ‘agar’ or ‘agar-agar’ was used for certain East Indian edible Rhodophyceae of the genus Eucheuma and probably, by extension, for other seaweeds. Alga is manufactured mainly from Gelidium, Gracillaria, Pterocladia, Phyllophora. Last species found in Black Sea and Russia, Romania and Turkey use this species for production of agar.

Fig. Phyllophora nervosa, a Red Algae found in Black Sea and using for agar production Carrageen

This is extracted from Rhdophycean alga Chondrus and to a lesser extent from Gigartina. Chondrus, growing in the interdital zone is very abundant in the Canada and is harvested there, using wooden rakes. Most of the processing is done in the United States. In the presence of potassium, these compounds gel and are used like alginates to stabilize emulsions and suspend solids, etc., in the food, textile, pharmaceutical, leather and brewing industries.

7.2 Alginic acid (alginate) These are extracted from Phaeophyta, e.g. from Laminaria, Ascophyllum, Macrocystis, Ecklonia, Eisenia. The alginic acid occurs in the middle lamella and primary walls of these algae, while cellulose is found in the secondary walls. Its structure is very similar to that of cellulose and pectic acid.

The use of alginates in industry depends on the chemical and physical properties of the compounds, e.g. they are non-toxic, highly viscous and readily form gels. Alginates using following areas:

Food industry (filling creams) Cosmetics (e.g. hand creams) Textile industry (as printing pastes) Rubber industry in latex production As emulsifiers (e.g. in ice cream, synthetic cream, processed cheese, pharmaceutical

emulsions, polishes, emulsion paints) As gelling agents in confectionary and meat jellies. As dental impression powders Ceramic industry (in glazes) Paper industry (as surface films) Food industry (as alginate films in the sausage case)

7.3 Diatomite During Tertiary an Quaternary times, the production of diatoms has been so great in some regions that large sedimentary deposits have been formed. The siliceous cell walls are relatively insoluble and hence these sediments accumulated in marine and freshwater basins and some are relatively uncontaminated by clay, etc. In theses areas the thick deposits are scooped up with large earth-moving equipment and processed in a modern chemical engineering plant. The natural deposit contains a high proportion of silica. When processed it is chemically inert and is mainly used as a filtration aid, as a filler in paints, varnishes, and paper products an in insulation materials, particularly those for use at high at high and low temperatures.

It is particularly important in the sugar refining and brewing industries. In wine making, diatomite added as a filter aid, sometimes at as many as four stages in production. It is also as a filter in the production of antibiotics when the waste mycelium, etc., is removed. In many industrial processes the recovery of chemicals and reclamation and recycling of water is aided by the addition of diatomite. Alfred Nobel made use of diatomite as an absorbent for nitro-glycerin in the manufacture of dynamite, but it has now been replaced by other substances. Diatomaceous earth was used to make lightweight bricks in the building of the 32,6 m dome of the Cathedral of St. Sophia in Istanbul in A.D. 532.

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7.4 Other aspect of using algae

7.4.1 Fertilizer In a small way algae are used as fertilizers on farmland close to the sea. The larger brown and red algae are used as organic fertilizers; these are usually richer in potassium but poorer in nitrogen and phosphorus than farm manure. The weed is usually applied direct and ploughed in, but it also been processed into a seaweed meal for transport inland. A concentrated extract of seaweeds is sold as liquid fertilizer.

7.4.2 Fodder In maritema districts seaweeds have been used directly for animal fodder with beneficial effects; this effects may be related to the high vitamin and micronutrient content. The time of collection, drying, preparation, and the storage of the meal all affect the nutrient value, particularly the vitamin content, which can be halved in Fucus meals stored for five months. The ascorbic acid (vitamin C) content is at a maximum in early summer and a minimum in mid-winter.

Many fish, both marine and freshwater, feed on planktonic or attached algae. Diatoms are apparently easily digested by most fish, although the silica frustules are not utilized. Young marine fish are also known to feed extensively on benthic microscopic algae particularly those attached to sand grains.

7.4.3 Food Only in the Far East have algae been regularly used for human food. In the pacific Islands the raw algae, usually species of Rhodophyta, but also Chlorophyta and Phaeophyta, are chopped and added to other dishes. Young stipes of Laminaria and the reproductive leaflets of Alaria have also been eaten without much preparation in Europe and N. America. The most prolific users of seaweeds are however the coastal population of china, Japan and o tropical Pacific Islands, where numerous genera are used. The commonest are species of Porphyra and of Laminaria.

The extensive experiments on mass algal culture show without doubt that if necessary, algae, particularly Chlorella, could be grown and processed into food. Deleterious effects

Under certain circumstances and in particular during periods of mass production, algae or their toxic products may cause injury or even mortality amongst animals. In fish ponds and in nature, mass growth of filamentous and mucilaginous species results in a physical smothering and/or oxygen depletion leading to death of young fish fry. The most widespread harmful affects are those caused by algal blooms.

In the oceans, species of Dinoflagellates often cause the red discoloration known as “red tides,” while in freshwaters the blooms are usually due to Cyanobacteria, although some of the most detrimental are caused by minute flagellates. Strong poisons have been extracted from algae causing water blooms, and from shellfish feeding on the algae. It has been shown that mussels can store large amounts of these toxins, and when eaten by man, these cause paralytic shellfish poisoning.

In freshwaters the most common deleterious algae are species of Cyanobacteria (Microcystis, Aphanizomenon, Anabaena, etc.) killing aquatic animals, farm animals and birds, especially those which drink the surface waters where there is the greatest concentration of plankton during an “algal bloom.”

8 BIOLOGICAL ASSESSMENT IN WATER POLLUTION. The effect of pollution on rivers or standing waters can be measured chemically, since it usually involves the addition of toxic substances or of organic wastes which on decomposition deplete the oxygen supply. However, the deleterious effects are on the organisms and the degree of pollution can often be measured most easily by a biological analysis, in which algae are important indicators. Algae are sensitive to the degree of reducing or oxidizing activity in the water. In the reducing zone, where oxygen is completely depleted, algae are subordinate to bacteria, especially sulphur bacteria. However, even in this type of water (polysabrobic), a few algae may survive, e.g. Oscillatoria chlorina, Spirulina jenneri, Euglena spp. and a few other flagellates. In the next zone (mesosaprobic), oxygen is not completely depleted and algae can grow; these zones succeed one another down a river from the source of pollution, or spread out in concentric zones in ponds and lakes. Two subdivision of this zone are often used and it is only the α-mesosaprobic zone which is polluted in the common sense of the word. Here Oscillatoria spp., Nitzchia palea, Gomphonema parvulum appear and indicate the improvement in the water. The β-mesosaprobic zone may be still polluted on a chemical basis, but so far as the algae are concerned, it supports a rich flora comparable to that of many eutrophic waters. Further degreesof purity are found in oligosaprobic waters (i.e. in the upper reaches of streams or in oligotrophic lakes) and in katharobic waters where organic matter es at a minimum (e.g. in spring waters).

Katharobic Oligsaprobic β-mesosaprobic α-mesosaprobic Polysaprobic

Increasing organic matter

Saprobic zones

In water polluted by toxic chemicals, even the bacterial flora may be killed and no breakdown of the effluents is possible. Short-term pollution of this type may be difficult to detect chemically since the effluent may pass away rapidly but biological assessment will reveal the extent to which the algal flora has suffered.