1.     The cell wall was first observed by: Robert Hook

2.     The book Micrographia was written by: Robert Hook

3.     The main component of the cell wall is : Cellulose

4.     The cementing substance between the two cells is known as :

Middle Lamellum                                      

5.     Middle Lamellum in plant cell walls is made up of :

Calcium and Magnesium Pectates

6.     Unit membrane model is also known as : Robertson’s Model

7.     Movement of molecules from their higher concentration to lower concentration is called: Diffusion

8.     Chromosomes are located at the equatorial place in : Metaphase

9.     Cell Theory was proposed by : Schleiden & Schwann

     The structural and functional unit of an organism is known as : Cell

Algae

ALGAE

It is very difficult to define Algae. According to Fritsch algae must include all holophytic organisms that fail to reach the higher level of differentiation, charactristic of higher plants. G.M.Smith defines algae as simple plants with autotrophic mode of nutrition. Sharma defines algae as an assemblage of chlorophyll bearing autotrophic Thallophytes bounded by a cell wall made up of pure or mixed carbohydrates. The study of Algae is known as Algology or Phycology.

Phycology.(Gk: Phycos-Sea weed & ology - Study)

Linneaus (1754) coined the term Algae.

I.Habit & Habitat

Algal members are predominantly aquatic

1. Aquatic Algae:

Completely submerged or free floating.

Fresh water algal forms- Chlamydomonas, Volvox, Hydrodictyon.

Slow Running Water- Cladophora, Oedogonium, Ulothrix.

Sea water- Phaeophyceae, Rhodophyceae members.

Planktons-Free floating -  Chlamydomonas, Cosmarium.

2. Terrestrial Algae:

Algae found beneath the moist soil surface - Nostoc, Anabaena, Euglena.

Algae found on the moist surface- Vaucheria, Botrydium, Oedocladium, Fritschiella.

3. Aerophytes: Trentepohlia is found on the bank of trees in moist and humid

conditions. Phermidium, Scytonema and Haplosiphon have been observed to grow on bark of trees along with Bryophytes.

4. Cryophytes: Haematococcus nivalis gives Red colouration to Arctic and Alpine

regions, Chlamydomonas yellowstonensis gives green colouration to snow.

Those algae which are found on snow and not on ice some species of Raphidonema, Chlamydomonas.

Those algae which grow only on ice and result in icebloom - Ancylonema, Mesotaenium.

Those algae which  can grow on snow and ice both –Trachiscia and Chlamydrocystis.

Those algae which are not true cryophytes and have their temporary growth on ice or snow. Eg: Phormidium.

5. Thermophytes: Temperature upto 85oC – Few genes belonging to family Chrococcaceae, Oscillatoriaceae.

6. Algae of unusual habitat:

i).  Halophytic algae : Lives in Saline Water -  Dunahiella, Stephanoptera.

ii). Lithophytic algae            : Lives on Rocky substaratum - Ectocarpus,Polysiphonia.

iii). Epiphytic algae  : Lives on some other plants - Coleochaete,

iv). Epizoic algae      : Lives on some other Animals –

  Cladophora, is found on snails.

v). Endozoic algae    : Lives in some other Animals -

  Zoochlorella is found inside Hydra viridis.

vi). Parasitic algae     : Lives as a Parasite –

  Cephaleuros viresceus, causes Red Rust of Tea

vii). Symbiotic algae : Lives in Symbiotic Association

  Nostoc found in thallus of Anthoceros and Notothylus.

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II. ALGAE - CELL STRUCTURE

Mostly Prokaryotic (Cyanopheceae, Myxophyceae and Blue Green Algae) and Eukaryotic (In Remaining Algal Groups) cell structures can be observed in Algal members Mesokaryotic cell structure (Nucleus is present, but chromosomes are without basic histone  proteins)  is present in Dinophyceae.

1. Cell Wall: The cell wall is made up of two layers. Outer amorphous pectic substances and the inner fibrillar cellulose layer. But cell wall composition is different in different Algal members.

Xanthophyceae – Solely Pectic Substances  

Phaeophyceae – Hemi Cellulose, Alginic Acid , Fucoisan

Diatoms – Silica and Pectin

BGA – Mucopolymers.

2. Flegella : Motile vegetative or reproductive cells are found in all groups of algae except Rhodophyceae and Cyanophyceae . Their motility is due to Protoplasmic appendages called flagella .

Flagella are of following types :

(i)              Whiplash or Acronematic flagella : Smooth surface and abruptly terminates in a fibril.

(ii)            Tinsel or Pleuronematic flagella: Flagella covered with fine filamentous appendages called Mastigonemes or Flimmers .

They are further divided into three categories on the basis of arrangement of Mastigonemes:

(a)  Pantonematic: Mastigonemes are arranged on either side of the flagellum .

(b)  Stichonematic: Mastigonemes develop only on one side of flagellum .

(c)   Pantacronematic: Pantonematic flagellum is with a terminal fibril

Isokont: flagella of cell are similar. (Chlorophyceae) .

Heterokon: flagella of cell are dissimilar (Pheophyceae , Xanthophyceae) .

3. Plastids and Chromatophores:  Plastids with Chlorophyll a and b are called

Chloroplast , while those lacking chlorophlll b are called Chromatophores . The chloroplast may be cup-shaped (Ulothrix, Chlamydomonas) or Discoid                                                                                                                                                                                                  (Vaucheria , Chara) or Reticulate (Oedogonium) or Spiral (Spirogyra) or Stellate (Zygnema).

4. Pigements: The various pigments associated with algal members are listed below

(a).Chlorophylls: Chlorophyll – a (all groups) Chlorophyll - b (Chlorophyceae); Chlorophyll – c (Phaeophyceae, Cryptophyceae, Bacillariophyceae & Chrysophyceae), Chlorophyll – d (Rhodophyceae) Chlorophyll  - e (Xanthophyceae).

            (b).Cartenoids: Carotenoid include Carotenes and Xanthophylls.

            Xanthophylls: More than 20 types of Xantophylls are present.

            Fucoxanthin - Phaeophyceae, Diatoms.

Myxoxanthin-Cyanophyceae.

            Carotenes: 5 Types.

             ∞-Carotene- Chlorophyceae, Cryptophyceae and Rhodophyceae.

γ- Carotene- in all groups except Cryptophyceae

             c- carotene- chlorophyceae

e- carotene- Diatons, phaeophyceae,BGA

flavacene- BGA

(c) Phycobilins: Water soluble pigments.

            Red (phycoerythrin) and blue (phycocyanin)

Rhytophycene and BGA respectively. They act as light harvesting pigments in photosynthesis.

5. Pyrenoids: Proteinaceous bodies found either within or the surface of plastids.Concerned with storage of starch in green algae or to store similar food in other algae. Number may vary from one to many.
6. Storage Products: Chlophyceae(starch) Rhodophycene(Floridean starch) BGA(Cyanophycean starch) Phaeophycene(Laminarin & Mannitol)Chrysophyceae,Diatoms, Xanthophyceae(Lencosin)
7. Golgibodies: They may be  at base or at  the nuclus(vx,Euena oathe plastids.t  Blue green Algae.
8. Mitochondria: Present in all algal members concerned with respiration.
9. Vacuoles: Osmotic functions or absorption of solutes and water. In motile algae, two types of vacuoles are recognized. (i) The simple/contractile vacuoles and

      (ii) Coex vacuoles.

10. Eye- spot or Stigma: The motile vegetative and reproductive cells of algae have a pigmented spot known as eye- spot or Stigma. It is a photo receptor organ.
11. Nucleus: Most of the algal members are uninucleate, but coenocytic siphonales, cladophorates, charales, heterosiphonales

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III. THALLUS ORGANISATION OF ALGAE

The Thallus structure is basically of two types:

The Unicellular and Multicellular forms.

1.Unicellular forms:  The thallus is a single cell and the unicellular forms may be motile. Unicellular forms can be classified into two types.

(a).Motile Unicellular forms:

Unicellular motile forms are found in all classes except Bacillariophyceae, Phaeophyceae, Rhodophyceae and Bluegreen Algae. The flagella may be one (Chromulina) or two and equal (Chlamydomonas) or two unequal (Cryptomonas). In some forms fine protoplasmic projections called Rhizopodia are present(Chrysamoeba).In some flagellates,external to the periplast there is a calcarious envelope and they are called encapsulated forms(Chrysococcus)

(b).Non-motile or Coccoid forms:

These forms are without flagella and are sedentary. They are of several shapes. The non motile forms may occur in several classes of algal like Chlorophyceae (Chlorella), Cyanophyceae (Spirulina), Diatoms, Xanthophyceae and Rhodophyceae (Porphyridium). The smallest known Eukaryotic algae is Micromonas pusilla.

(2) Colonial forms: A colony is an aggregate of cells enclosed in mucilage envelope. There are four types of colonial algae-Coenobial, Palmelloid, Dendroid and Rhizopodial Forms.

(a)Coenobium:

A colony with definite number of cells and having a constant shape and size is called coenobium. This may be motile having flagella (Volvox) or non motile (Hydrodictyon).

(b) Palmelloid colony:

The colony in which there is no fixed number of cells and the non-motile cells are embedded in amorphous mucilaginous covering (Aphanotheca of Cyanophyceae and Tetrapora of Chlorophyceae).

(c) Dendroid colony:

Dendroid means tree like and the cells are joined in a branch like manner by localized production of mucilage, at the base of each cell. e.g. Eebellocystis of Chlorophyceae, Mischococcus of Xanthophyceae.

(3) Filamentous forms: Filamentous forms are common in algae. In a filament the cells are joined end to end. In Cyanophyta, a filament consists of a trichome of uniseriate cells and a mucilage sheath. The filaments may be branched, simple branched or heterotrichous.

(a)  Unbranched filaments:

In a filament cells are arranged in uniseriate. These are common in Chlorophyceae, Xanthophyceae and Cyanophyceae. They may be attached with the basal cell called “hapteron” as hold fast to the substratum (Oedogonium) or free floating (Spirogyra). Some filamentous forms exhibit distinct polarity with trichome tapering towards the tip. Eg:Rivularia.

(b)  Branched filaments:

Branched filaments are of two types. True and False branching. In most of the forms true branching is due to lateral out growths developing into branches. During growth, the lateral branch is pushed aside. This is called evection and due to evection the branching looks like dichotomous (Cladophora). False branching occurs in Scytonemataceae of BGA, where the trichome breaks due to degeneration of an intercalary cell and the broken ends grow out of the mucilage sheath and appear like branches.

(c)   Heterotrichous forms:

This habit is the most highly evolved types of filamentous forms in algae. The thallus is differentiated into two parts, a prostrate system of creeping filaments. Eg. Coleochate, Fritsch considered that the first land parts might have arisen from the algae exhibiting heterotrichous habit.

(d)   Siphonous forms:

The thallus in non septate,multi-nucleate with a large central vacuole. It is coenocytic as ther are no septa. Siphonacoccus forms are found in Chlorophyceae and Xanthophyceae. The simplest siphonaceous thallus is represented by Protosiphon, consisting of vesicle and a rhizoid. In Vaucheria there is a branched tubular thallus which is coenocytic and aseptate.

(5) Pseudoparenchymatous forms:

This habitat develops from close juxta position of either a single main filament or a number of such filaments. In unaxial pseudoparenchyma there is a close apposition of branches of a single filament. Eg: Batrachospermum. In multiaxial pseudoparenchyma, the branches of many axial filaments give rise to lateral branches. These branches become compact and is called cortex E.g. Codium and Polysiphonia.

(6) Parenchymatous forms:

This habit is derived from the filamentous thallus as a result of vegetative divisions taking place in more than one plane. The thallus may be foliose and flat (Ulva) or tubular (Enteromorpha).In brown algae the parenchymatous habit is well developed. The thallus is differentiated into central medulla, middle cortex and outer meristoderm. Some of the example are Laminaria,Macrocystis Fucus and Dicyota.Folioceous plant body is also found in Porphyra of Rhodophyceae.

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IV. CLASSIFICATION OF ALGAE

Algae consists of a large number of  diverse forms which vary in shape and size. There are two schools of thought regarding the classification of algae.

According to the first view, the algae is equivalent to a division, and therefore it can only be further divided into classes(-phyceae) and not into divisions(-phyta). This view was supported by Fritsch and his followers. It is based on the following characters.

(i)              Chlorophyll - a is common to all algae and so there is definitely a common origin from a common source, therefore, they all belong to the same group.

(ii)            Internal structure of flagella is similar in all.

(iii)          Product of assimilation (reserve food) may be different but the process of assimilation is same in all.

(iv)          Methods of reproduction are almost common to all.

 According to the second view, the algae is above the rank of a division. So it should be divided into some divisions (=phyta) and then each division into one or more classes. This view was supported by workers like Smith ,Papenfuss, Prescott. Supporters of this view, considered the following criteria to their classification.

(i)              Pigments are different in different phytas(division)

(ii)            Product of photosynthesis is different in different divisions.

Papenfuss proposed that the word “phyco” must be incorporated before “phyta” especially because of their link with algae.

Criteria for classification:

Generally a combination of a few or more of the following characters, are considered by the algal taxonomists while classifying algae. They include

(i)              Pigments: Their complement,relative amount,kinds,chemical composition.

(ii)            External forms: Size,shape,appendages and other structures.

(iii)          Chromatophore shape: Cup shaped, stellate, reticulate, discoid,spiral,girdle shaped.

(iv)          Reserve food products: Strach,oil globules etc.,

(v)            Flagella: Structure,type,number,position,anatomy and invertion on the body.

(vi)          Cell wall: Chemical composition

(vii)        Nucleus: Presence or absence of a definite nucleus.

(viii)      Chromosome: Number, arrangement, shape.

(ix)          Life history & Reproduction: Tyupe of life history, method of reproduction, shape of reproductive bodies, presence or absence of sexual reproduction etc.,

(x)            Ecological data: fresh water,Marine water etc.,

F.E.Fritsch System of classification:

Fritsch’s classification: F.E.Fritsch (1935, 1945) proposed a most comprehensive and anthroritative classification in his book “structure and reproduction of algae” . He considered that as a group algae deserve the rank of division. He divided it into 11 classes based on pigments,reserve food materials and flagellar types. The following are classes.

(1)  Chlorophyceae

(2)  Xanthophyceae

(3)  Chrysophyceae

(4)  Bacillariophyceae

(5)  Cryptophyceae

(6)  Dinophyceae

(7)  Chloromonadinae

(8)  Euglineae

(9)  Phaeophyceae

(10) Rhodophyceae

(11) Myxophyceae

G.M.Smith’s Classification (1955):

Smith proposed the classification of algae taking into consideration the evolutionary principles proposed by Fascher (1914). He did not use the term algae. He classified spore producing plants into various divisions.

(1)  Division: Chlorophyta

Class 1: Chlorophyceae(Grass green algae)

Class 2: Charophyceae(stoneworts)

(2)  Div: Euglenophyta

Class 1: Euglenophyceae(Euglenoids)

(3)  Div: Pyrrophyta

Class 1: Desinophyceae(Dinophysids)

Class 2: Dinophyceae(Dinoflagellates)

(4)  Div: Chrysophyta

Class 1: Chrysophyceae (Golden brown algae)

Class 2: Xanthophyceae(Yellow green algae)

Class 3: Bacillariophyceae(Diatoms)

(5)  Div: Phaeophyta (Brown algae)

Class 1: Isogenerateae

Class 2: Heterogenerateae

Class 3: Cycyclosporeae

(6)  Div: Cyanophyta

Class 1: Myxophyceae

(7)  Div: Rhodophyta(Red algae)

Class 1: Rhodophyceae

(8)  Div: Algae of uncertain systemic position

Chloromopnadales

Cryptophyceae.

G.E.Papenfuss(1955) proposed a classification of algae based on phylogenetic relationships. He recognised 8 phyla and 12 classes listed below.

Phylum 1: Chlorophycophyta

Class: Chlorophyceae

Phylum 2: Charophycophyta

Class: Charophyceae.

Phylum 3: Euglenophycophyta.

Class: Euglenophyceae.

Phylum 4: Chrysophycophyta

Class: Xanthophyceae; Chrysophyceae, Bacillariophyceae.

Phylum 5: Pyrrophycophyta

Class: Dinophyceae; Cryptophyceae, chloromonadophyceae.

Phylum 6: Phaeophycophyta

Class: Phaeophyceae

Phylum 7: Schizophycophyta

Class: Schizophyceae

Phylum 8: Rhodophycophyta

Class: Rhodophyceae.

Christensen (1964) proposed a new scheme of primary classification of algae into Prokaryota and Eukaryota. On the basis of difference between the prokaryotic and eukaryotic cells.

G.W.Prescott (1969) empasised the presence or absence of true nucleus in the algal cells for their classification along with other characters. Viz. Pigmentation, biochemical nature of cell wall and reserve food material and divided algae into nine phyla and fourteen classes.

F.E.Round (1973) also recognised the importance of presence or absence of well organized nucleus in algal cells in the classification of algae along with their phylogenetic relationships and other characteristics. He made certain modifications in the scheme proposed by Fritsch and raised the rank of classes of Fritsch to phyla. Besides this. Round placed BGA in a major group prokaryota which was put at the top whereas Fritsch has placed them near Rhodophyceae.

The modern algologists classify these plants of algal organization into 11 divisions, namely, Cyanophyta, Chlorophyta, Xanthophyta, Chrysophyta, Bacillariophyta, Pyrrophyta, Cryptophyta, Euglenophyta, Phaeophyta and Rhodophyta.

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VII. REPRODUCTION IN ALGAE

The chief object of reproduction is the perpetuation of the species and consequently the increase in number of the individuals of a species. There are two main types of reproduction, Asexual and Sexual.

1. Asexual Reproduction: It consists in the separation from the parent of a highly specialized cell or a group of cells which directly develops into a new individual resembling the parent . Asexual reproduction is uniparentalwhich may occur in avariety of ways described below .

Spore formation: The spores are reproductive units specialized for asexual reproduction. Each unit can grow into a new organism by itself . It involves no sex and there is only one parent. Algae reproduce asexually by producing  a variety of spores , some of them are

(a)  Zoo spores: These are motile , naked structures with two (Chlamydomonas , Ectocarpus) , four (Ulothrix) or many flagella (Oedogonium , Vaucheria) . Usually 2 – 32 Zoospores can arise single in a cell( oedogonium , ulothrix) Zoospores  may be diploid (mitotic divisions) or haploid (meiotic) , depending upon the nuclear division preceeding Zoospore formation. Zoospores fored in plurlocular sporangia of Ectocarpus are diploid where as the spores formed in unilocular sporangia are haploid. Zoospores are generally formed underextremely fovourable conditions. They are phototatic and are a means of dispersal in fluid medium. On germination , each Zoospore gives rise to a new plant.

(b)  Aplanospores: They are non – motile and constitute a normal means of asexual reproduction in the terrestrial species of the yellow green algae(vancheria). In some green algae they are produced under certain unusual conditions(Ulthrix and Microspaoa) .The aplanospores are regarded as Zoospores that have failed to develop flagella. Hence, these are considered analogous and non – homologous to endospores or exospores of Blue green algae. The walls of the aplanospores are thin as compared with the other non motile spores.

(c)   Hypnospores: Under certain more distressing environmental conditions the aplanospores in green algae secrete thicker walls around them. They are called the hypnospores. The hypnospores germinate into new plants with the return of conditions favourable for vegetative growth. In chlamydomonas nivalis the walls of the hypnospores become red due to the presence of haematochrome and represent the phenomenon known as the redsnow.

(d)   Akinetes: They are resting cells which may mainly serve as means of perennation rather than multiplication. In the formation of an akinete the entire proplast of the vegetative cell rounds off and the original parent cell wall, which also serves as the spore wall, becomes considerably thickened. These are formed after heterocysts in Blue green algae, in green algae like Pithophora and Cladophora these are commonly found.

(e)   Cysts and Statospores: Many flagellate algae and some filamentous forms produce cysts under unfavourable conditions and these cysts act as resting stages. Cysts are commonly found in diatoms. These spores may be smooth walled or the walls may be variously ornamented.

(f)    Neutralspores: In some algae, the protoplast of vegetative cells directly functions as spores and these are called Neutralspores(Asterocystis). In Eetocarpus, plurilocular sporangia produce diploid spores which are also called as neutralspores. Reproductionby neutralspores may be seasonal or may take place throughtout the season.

(g)   Monospores: These3 are haploid and naked and formed when the entire protoplast of a uninucleate sporangium gets transformed into a spore. These are generally formed in members of Rhodophyceae and Phaeophyceae.

(h)  Budding: Bold reported vegetative propagation in Protosiphon by the formation of buds. The vesicle proliferates a bud like outgrowth which is subsequently cut off by transverse septum. The bud grows into a new Protosiphon plant.

2. Sexual  Reproduction in Algae:

It involves the fuson of two specalised reproductive cells called gametes. The process of fusion is called fertilization and the product of fusion is called  the Zygote. Sexual reproduction is absent in Cyanophyceae. In general, the sexual reproduction in algae is mainly of two types, Isogamy and Heterogamy.

1. Isogamy:

It is the simplest and most primitive type of sexual reproduction. It consists of the fusion of morphologically identical gametes (Isogametes). This type of reproduction is found in simpler members of algae like Chlamydomonas. Isogamy remains absent in Siphonales and Phaeophyceae. In this type of sexual reproduction the gametes develop by a division of protoplast of the ordinary cell into several small bodies which are liberated alike to Zoospores. The gametes are motile, except in a few species of Chlamydomonadaceae, the gametes are always naked.

2. Heterogamy:

In this, fusing gametes are dissimilar ( dimorphic)

i.                Anisogamy:

When the two uniting gametes are dissimilar in size they are called Anisogametes. Sexual reproduction involving anisogametes is called Anisogamy. The smaller gamete is called Microgamete while the larger one is known as Macrogamete. The former one is compared a male gamete while the later one as a female.l. he vegetative cells n which gametes a produced are known as gameetangia.Sometimes amorphologically identical gametes behave differently and so show physiological anisogamy. E .g. Spirogyra and Ulothrix. Both kinds of gametes in anisogamy are motile.

ii.             Oogamy :

It is of advanced type of reproduction and in this kind both fusing gametes differ each other not only in size but also in motility behaviour, shape and structure. Oftenly they are formed specialized vegetative cells turned the sexorgan. Anthreredium (Spermatangium) and oogonium (carpogonium) are male and female sex organs respectively. The male gametes are termed antherozoids or sperms, while female gametes are called eggs. In Rhodophycea, the male gametes are non motile and are known as spermatia.

iii.           Aplanogamy:

When there is a fusion of two non-flagellated amoeboid gametes (aplanogametes), it is called Aplanogamy. Both the gametes are morphologically similar but differ in physiological behaviour. E.g. Spirogyra, Zygnema, etc.

iv.            Autogamy:

This type of reproduction is seen in diatoms in which the daughter protoplasts or the divided nucleus of a cell without liberation fuse.

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VIII. Economic  Importance of Algae

The Algae have been utilised either directly or indirectly for different purposes since time immemorial. No doubt that  algae are very prompt to show their useful effects too. Therefore , it has become necessary to find out it’s both types of uses – useful as well as harmful.

I. Useful Aspects :

1. Human Food :

Different kinds of Algae belonging to Chlorophyceae, Phaeophyceae and Cyanophyceae are eaten by the Japanese people. Most of these Algae are marine. Among these the most important is Asakussa. Nori preparation is made from Rhodophyceae member, Porphyra tenera. Besides the people of Japan, Pacific coasts of USA, the Dutch East indies, Burma, Siam, Borneo, Hawai, Indo-China and China also use sea weeds for food. The Algae which are used by all these countries are Alaria, Chorella, Chondrus, Nostoc, Codium, Porphyra, Rhodomenia and Ulva. These Algae not only form an important ingredient of soups, but are also use dfor flavouring the meat. In Brazil and also in South American countries floating colonies of Nostoc on boiling are used as food. These Algae are very rich in Proteins, fats and vitamins. Dried Chondrus crispus is used in puddlings and jellies in Ireland. Japanese fisher men eat Sargassum enerve, Alaria, Arhothomus and Laminaria are employed to make a common vegetable of Japan called Kombu. Chlorella is another important Alga cultivated for food in Germany, Japan and USA. Chorella can be compared with Soyabean and Spinach nutritionally. In Scotland Rhodomenia polmata is chewed like Tobacco and Laurencia pinnatifida is consumed as a condiment. Chlorella and Scenedesmus are used as dried food. Agar- agar whiich is prepared from Gracillaria is widely used in making ice-creams, jams and jellies. There are also some reports about fresh water filamentous algae such as Oedogonium and Spirogyra, which are occassionally employed in the preparation of soups.

2. Animal Food:

i. Fodder: Denmark, France, Newzeland, Norway and USA are the countries where sea weed are frequently used as fodder for sheep, goat, cattle and poultry. Sea weed fodder is very much nutritious because of its high vitamin and mineral content. Sargassum, Fucus, Laminaria, Rhodomenia, Ascophyllum etc., are used as stock feed. Macrocystis is eaten by chicken. The milk produced by those cows that feed such sea weeds, is richer in fact content than those feed on conventional fodder. Similarly hens eating such sea weed meal also produce eggs rich in Iodine.

ii. Fish and other Animals Food: Fishes and their products ( Fish oils) are used by man in various ways. Fish inturn depend upon various Algae for their food. Algae both planktonic and attached forms in sea and in fresh water are used as primary food for fishes and other aquatic animals. Cladophora, Oedogonium, Pithophora, Spirogyra and Ulothrix are common fresh water algae, used by different types of fishes as their food. The placing of Bamboo bunches in fish pond is one of the practical methods to increase algal feed because by doing so, a very large surface becomes available for the growth of algal epiphyte.

3. Industrial Uses ( Commercial Products):

i. Agar-Agar : It is cheifly obtained on commercial basis from seaweeds like Chondrus, Gelidium, Gigartina, Gracillaria, Pterocladia, Phyllophora, Sunaria. Agar is usually emplpyed for culture medium of Bacteria, Fungi, Algae and Tissue culture. It serves as solidifying agent. Chemically agar is a Galactan, a complex of Carbohydrate composed of Galactose molecules and not subjected to breakdown by most of the Bacteria. It is usually used in 1.5 to 3 % . Besides solidifying agent, agar is employed in cosmetic, pharmaceutical, leather and textile industries. It is also widely used in the preparations of ice creams, jellies, soups and sauces.

ii. Carrageenin ( Caroganin) : Chemically it is very alike to Agar. It is found as cell wall polysaccharide esterified with Sulphate. This is a product of several seaweeds but principally Chondrus crispus, occassionally Gigartina are also used. It is mainly employed in the preparations of tooth faste, cosmotics, paints and also utilised in the textiles, leather brewing and medical industries. It is given to the patients of cough and is used as pharmaceutical emulsifier too.

iii. Minerals and Elements:

(a) Iodine: The sea weeds like Ecklonia, Eisenia, fucus and Laminaria are the sources of this chemical. Iodine is an important comeponent of thyroid harmones, hence tremendously used in chemotherapy of thyroids. In Japan 5-7 % of world production of Iodine comes from sea weeds.

(b) Bromine: Sea weeds like algae Rhodomella and polysiphonia are used to yield Bromine on moderate scale.

(c) Alginic Acid (Algin): It is obtained from Ascophyllum and Laminaria. This is used in making water proof varnishes, dyes, artificial fibres, type-writer rollers, vulcanization, manufacture of inflammable films and to control blod flow during surgery. In India the fucaceae is the chief source of algin but various species of Encoeliaceae and Dictyotaceae are also fair sources.

(d) Miscellaneous minerals and Elements: Copper, Chromium, Cobalt, Iron, Magnesium, Molybdinum and Vanadium may also be obtained from sea weeds. These chemicals are employed as supplements to fodders and fertilizers. Besides these the brown sea weeds also contain soda and Potash and even Ammonia if carefully processed.

iv. Mucilage: This is employed in the manufacture of felt hats as a stiffing agent and is obtained from Chondrus. The mucilage obtained by these sea weeds is charcterized by the properties of agar and is also employed as ingredient in cosmetics, shaving creams, shampoos and shoe polish.

v. Alginates: These are the salts of alginic acid, contined in the cell wall of Phacophyta. The main source of them is the sea weeds like Cystoseira, Ecklonia, Fucus, Laminaria, Lessonia and Macrocystis. They are extensively employed in the formation of plastic articles, flame proof fabrics and in medical use. They are also utilized in the function of soups, sauces, cosmetics, paints and polishes.

vi. Diatomite: Diatoms and their fossilized accummulation called diatomaceous earth are very useful for their different roles played by them. There may be about 40 million diatom frustules (walls) in a cubic inch, yet a cubic feet of diatomaceous earth may weigh as little as 4kg. Due to their porosity and insolubility they make an excellent filter for oils, cleaning solvents, plastic, rubber and other substances. They are also resistant to most acids and corrosive substances. Diatomaceous earth is useable in the formation of high temperature furnaces as these are light weight strong, fire proof and a good insulator.

vii. Soap, Alum and Glassware: A few years ago Kelps of Phacophyceae were employed as a source of soda in manufacture of soap, alum and glassware. But the cost being high, now a days this is not employed.

4. Agricultural uses:

i. Fertilizers and Manure: Algalmembers are being used as fertilizers and manures due to having more Potassium, Phosphorus trace elements and growth substances. The sea weeds manure is poorer in Nitrogen and Phosphorous in comparison to farm manure. But Blue green Algae containmore nitrogen and phosphorous than sea weeds. Thus a mixture of sea weeds and cyanophycean manure may be an ideal fertilizer. The people of Irish use Fucus as a source of manure on large scale. Lithophyllum and Lithothamnion being lime depositing algae are employed to increase the amount of lime in fields. In the Sambhar Salt Lake (Rajasthan) Anabaenopsis and Spirulina are cultivated in good numbers and are used by local farmers as green manure.

ii. Nitrogen Fixation: In addition ot Photosynthestic activities many algae especially Blue Green Algae have the ability to assimilate or fix the elementary Nitrogen of the atmosphere. Different species of Oscillatoria, Anabaena, Scytonema, Cylindrospermum, Nustoc, Microcystis are common which have been studied in relaition to Nitrogen fixation. Some Cyanophycean algae are ususlally found in symbiotic association with other types of organisms to serve the purpose of nitorgen fixation.

iii. Soil Formation:  Some symbolic algae associated in Lichens are pioneers of plant succession at bare hill area and thus help in soil formation. Crustore lichens are regarded as pioneers in this respect.

iv. Soil Conservation: Some algae like Anabaena, Lyngbya, Symploca and Tolypothrix very soon form a layer on the soil and this algal layer may contribute in the prevention of soil erosion caused by natural and other agencies.

v. Soil Reclamation: Several Bluegreen Algae like Anamaena, Aulosira, Cylindrospermum, Nostoc Scytonema are promissing in reclamation of “usar”/ “rch” (alkaline soils). These can change usar soil into fertile and cultivable land.

5. Medical Uses:

i. Antibiotics: Algae may also be employed for the extraction of antibiotics. An antibiotic known as Chlorellin has been obtained from Chlorella. This antibiotic is not as effective as Pencillin. Chlorellin is effective against Escherichia coli, Shigellla dysentriae and Staphylococcus aurens. Extracts of Dunaliella inhibits the growth of Closteridium. Antimicrobial properties are also depicted by the extracts obtained from Ascophyllium, Laminareae and Polysiohonia. Niitella causes death for mosquitoes in ponds. Therefore they are cultivated to control the malaria.

ii. Medicines: Digenia simplex is used as a vermifuge in Japan and China. Fucus, Ulva and Sargasum are also employed in sccrofulous lymphatic and glandular disorder. Agar is used in the preparation of pills and ointments. Extracts from Corallina and Codium are used for the treatment of Kidney, bladder and lung diseases.

iii. Vitamins: Some sea weeds and fresh water algal forms are rich in vitamin A,B,C and E. Vitamin A is contained in the diatom. Ulva and Porphyra contain Vitamin B. Vitamin C is found in Alaria. Like most of other algae, Chlorella contains most of known vitamins such as Carotine, thiamin, riboflavin, niacin, pyridoxine, panthothenic acid, Choline, Biotine, Vitamin B₁₂ and lipoic acid. It has been studied that 1/8kg of chlorella supplies all the daily minimal human vitamins except Ascorbic acid. Phytoplankton is the basic source of vitamins except Ascorbic acid.

6. Miscellaneous Uses:

i. Sewage Disposal: Chlorella, Chlamydomonas, Scenedesunus, Englena are inoculated in the sewage and help in decomposition of sewage by releasing Oxygen. Further these algae (sewage algae) may also be used as food by animals as green manures, etc.

ii. Growth harmones:  These are some reports regarding the presence of auxin in the cell wall and protoplasm of Valonia macrophysa and parific sea weeds like Fucus evanescens, Desurarestia aculeata.

iii. Light weight buildings: Recently the people of Germany are employing some sea weeds mixed with cement in order to prepare their buildings light in weight and heat resistant.

iv. Ornamental uses: Botrydium and Spirogyra are some of the algae which are used to be grown in the garden ponds for their good looking habit. Some algae like Volvox, Nostoc and Hydrodictyon look wonderful objects when seen with naked eye.

v. Origin of Petrolium and fuel gase: The organic compounds derived from the dead bodies of sea weeds and animals accumulated at the bottom of the ocean and were buried in the course of time by sedentery action. Later these compounds in anaerobic environment were decomposed and changed into oil and gas.

vi. Space travel: Biological system with a complete recycling of Chlorella Pyrenoidosa may be employed for the manufacturing of food taking CO₂ and giving out O₂ as a by product for use.

vii. Filteration of water: Because of sand like filtering quality the diatomaceous earth is thought to be besst filter for the filteration of water.

viii. Test Organisms: Chlorella, Scenedesmus are common test organisms which can be employed in Physiology, Biochemistry, Cancer timnological and Oceanographic research. Acetabularia and Valonia are preferably used in research to study nucleocytoplasmic relation.

II. Harmful Aspects

(1) Damage to Buildings: A good deal of damage to buildings including historical monuments is caused by the growth of algae and lichens.

(2)  Damage to Ships: Some marine algae usually grow on the metal and wood work of ships and boats and cause damage to them by corroding and fouling and consequently thus shorten the life of ships.

(3) Ddamage to textiles: Some algae (Blue green algae) also show their damaging effects upon various kinds of textiles, cordage and tentage.

(4) Damage to human health: There are some Phytoplankton algae are harboured by the larvae of mosquitoes which cause malaria and filaria. The dinoflagellates (Gonyalanx entenella) produce endotoxins which are harmlessto fishes when they are taken by them. But when these contaminated fishes are eaten by men, then they become very harmful and somtimes even cause death to human beings.

(5) Damage to animals and fishes: Some algae like Anabaena flosaquae, Glocotricha and Microcrystis aeruginosa produce exotoxins and endotoxins which are responsible for the death of several animals like sheep, cattle, cows, horses and birds, etc. Sometimes fishes are also caused death by algae which produce poisonous chemical substances. In this regard microcrystis can be cited as an example. Sometimes algal blooms reduce the O₂ contetn there by causing suffocation of fishes and finally responsible for the death of marine organisms.

(6) Mechanical injury: It has been observed that filamentous algae are found so abundantly in water forming a net behaviour that somtimes many fishes and other water animals are entangled and their direct death may be caused.

(7) Blocking of Photosynthesis: Epiphytic algae growing upon other plants and trees may stop photosynthesis.

(8) Recreational damage: Algae which are associated directly or indirectly with the loss of swimming and fishing values of ponds, pools and lakes involve Cladophora, Microcystis, Pithophora and Spirogyra. Further Anabaena Synedra are also responsible for the abnormal tastes and odours. Chlamydomonas, Chlorella and Oscillatoria by their presence in ponds also change the colour of water.

(9) Industrial damage: No doubt that some algal members also contaminate the water which when used spoils the quality of commercial products of food, medical and pulp industries.

(10) Parasitic algae: Some algae also develop as parasitic organisms. A few live as space parasites inside the tissue of higher plants e.g., Chlorochytrium leennae inside the tissue of Wemma. Some species are true parasites on various plants. Phyllobium dimorphum inside the leaves of Ajug: Phyllobium sphagnicolum is found on the leaves of Sphagnum. The family Blastodiniaceae (Pyrrophyta) includes several members of parasitic algae which attack several animals. Oodinium limneticum (Pyrrophyta) is an ectoparasite fresh water algal species which infects the grills and skin of various tropical fishes.

            Blastodinium is an endoparasite of the gut of Copepoda Cephaleuros virescens a fresh water algae (Chlophycene) is abundant in tropical and subtropical regoins and is practically a parasite growing on many plants, including mango, orange, lemon, grape fruit and tea (red rust of tea). There are some reports about Lyngbya (Blue green algae) and Chlorella (Chlorophycene) whic may cause certain skin infections.

(11) Pollution (Algal blooms): Some algae especially members of Myxophyceae during rainy season and spring are so much abundant that the water in the ponds, lakes and reservoirs become coloured attaining the colour of yellowish, greenish or bluish tinge. These manifestations of algal growth are called water blooms which are the most important source of algal pollution. Anabaena, Nostoc, Rivularia, Oscillatoria are Cyanophycean algae which frequently produce water blooms. In addition to Blue green algae, some green algae Spirogyra, Cladophora, Chlorella, Chlamydomonas diatoms and some golden brown algae due to their more production in water also become pollution causing agents.

            The bloom forming Blue green algae and red tide forming dinoflagellates produce algal toxins e.g., galtoxin which is a potent inhibitor of nervous system of multicellular organism. The mucilage in these algae serve as a home for many bacteria. These algae also produce toxic substances due to which pond water becomes contaminated and thus the water becomes unfit for the normal use.

            Anabaena, Asterionella, Dinobryon, Microcystis are algal members which by their metabolic or decomposition products produce abnormal tastes and odour in the water. Pond algae when are produced in abundant quantity, then they also change pH, CO₂, O₂ and bicarbonate contents of water. High temperature, low percentage of O₂, high percentage of CO₂, high percentage of N₂ and alkaline contents of lake favour the growth of Cyanophycean algae and water blooms. The death of fishes, cattle, birds, horses, sheep, pig, etc. Has been reported in foreign countries due to water pollution caused by algae. In India water blooms are very common in the ponds, tanks, pools, water reservoirs of villages or along the roads.

            The pollution may be avoided by:

i) Maintainance of aerobic conditions by checking purification of organic substance.

ii) Biological control: The virus – Cyanophase LPP-1 infects certain Cyanophycean algae.

Iii) Chemical control: The algicide (Copper sulphate) used in 0.25 to 9.5 ppm is very useful to control the growth of algae in ponds, pools, tanks and other kinds of water reservoirs. Sometimes the water is also chlorinated to kill algae and other microbes. Sometimes antibiotics, quinones and phenols are also employed to inhibit the tremendous growth of algae.