Algae

Algae

Introduction:

Latin:  Alga-‘sea weeds’

-Study of algae is known as Algology / Phycology.

Phycology- Gr.words(phykos-sea weeds, logous-study)

Algae is group of Autotrophic plants which fail to show cellular differebtiation and they have the unicellular sex organs. If the sex organs are multicellular all the cells will be equally fertile. (That’s why they have more population and capability of adaptability too)

Characteristics of algae:

1.      Algae are found in aquatic habitat both in freshwater as well as marine water. Some of them are also found in terrestrial habitat where the moisture content is high.

2.      The plant body of the thallus organization of algae ranges from unicellular microscopic form like chlamydomonous(fresh water) to multicellular complex giant form like Macrocystis(180m,marine)

They also show colonial form like volvox and branced or unbranced filamentous form like spirogyra,cladophora (branched filamentous form)etc

Some of them also have structures showing superficial resemblance with the root,stems and leaves of higher palnts.

3.      Algae lack conducting(vascular bundles) and mechanical tissue(strength providing tissue) so they are soft to touch

4.      The cell is eukaryotic and the cell wall is made up of cellulose along with other substances like Pectin,algin,chitin,fucoidin,etc. forming two layers.

5.      The reserved food material is starch but depending upon the classes other substances may also form the reserve food substances.

6.      The pigments present in algae are chlorophyll-‘a’, chlorophyll-‘b’, xanthophylls, carotenes and phycobillins/billiproteins. (for color and solar energy trapping pigments)

7.      Reproduction takes by vegetative asexual and sexual method.

-Asexual reproduction takes place by spores i.e. motile and non motile spores eg Zygospores

-vegetative reproduction by budding, fission etc

-sexual reproduction by fusion of gametes forms by two organisms of same species.

Classification of Algae:

F.E Fritsch(1935,1945) Phycologist, In his book the structure and reproduction in algae classified the broad group algae into Eleven classes on the basis of body structure,nature of reserved food materials,types of pigments,cell wall composition,methodsof reproduction etc.

Three Classes

1.      Chlorophyceae(Green algae)

2.      Phaephyceae(Brown Algae)

3.      Rhodophyceae(Red Algae)

1.Chlorophyceae:-

Largest class of algae and includes about 425 genera and over 7000 species.

Characteristics of Chlorophyceae:

a)      Habitat:

The members of chlorophyceae are found in fresh water and are cosmopolitan in distribution(found everywhere) some species are found in amrine water also whereas few species are found to occur in terrestrial habitat such as moist soil, moist and shaded part of trees, moist rocks etc.

-Freshwater form: chlamydomonas, spirogyra, pithophora, zygnema

-Marine water form: bryopsis, caulerpa, codium

- Terrestrial form:protococcus, trentipohlia.

b)      Habit:

The chlorophyceae show wide variety in the thallus organization of its constituent members such as;

-Unicellular,microscopic,motile form :chlamydomonas

-Unicellular, microscopic,non-motile form:chlorella, chlorococcum

-Multicellular/colonial, motile form: volvox,Eudorina,Pandorina

-Multicellular/Colonial,non-motile form: Hydrodictyon, Pediastrum

-Filamentous: Spirogyra,Oedogonium,Cladophora

Chara and nitella have developed structures

c)      The cell wall is double layered inner layer is made up of cellulose and the outer layer is of Pectose(Pectin+water=Pectose;slippery in nature)

d)      The reserved food material is starch.

e)      The pigments present in Chlorophyceae are chlorophyll-‘a’, chlorophyll-‘b’, xanthophylls, carotenes but Phycobillins/biliprotein are absent.

f)       Zygote represents the only diploid stage in the lifecycle of Chlorophyceae.

(plant body ois gametophyte forming gametes)i.e Haploid

Only zygote is representing sporophyte.

g)      The number and shape of chloroplast of different algae members of

Chlorophyceae differ from each other and this character is considered as one of the important character for the identification of the species

-Cup shaped :   chlamydomonas, volvox

-ring shaped : Ulothrix

-Reticulate : Oedogonium,Hydrodictyon

-Spirally coiled : Spirogyra

-Star-shaped : Zygnema

h)      The chloroplast contain distinct rounded proteinaceous  body inside them known as Pyrenoid which help in storing/storage of food material.

2. Phaeophyceae:

            Characters of Phaeophyceae:

1.      Habitat:  The brown algae are predominantly found in the marine water s\except few species such as Pleurocladia,lithoderma,spacelaria which are found in fresh water. They are generally found attached to the substratum with the help of specialized structure khown as ‘holdfast’ except few species as Sargassam (marine species)which form free floating masses. E.g other marine species are Fucus, Ectocarpus etc ; freshwater species are Pleurocladia,lithoderma,sphacelaria are fresh water.

2.      Habit: Brown algae are advanced group of algae so unicellular,colonial and unbranced filamentous forms are absent. They show Heterotrichous filamentous form as the simplest form.In Heterotrichous filaments,they have got two distinct types of brances.The random branches are absent.

3.      In some species the plant body is differentiated into –Holdfast,stem like stipe and flattened leaves like blades. They have superficial resemblance like above insome species like  Fucus.

4.      The cell wall is double layered. Inner layer os made up of cellulose and outer layer contains Fucidin (fucinic acid)and algin(alginic acid) along with Fucin.These can absorb large amount of water so water remain inside plant body fork very long period even during winter.

5.      The reserved food materials fare Laminarin and Mannitol along with this Chloride,Iodides,sucrose and glycerol are also Present.

6.      The pigments of Phaeophyceae are chlorophyll-‘a’, chlorophyll-‘c’,β-carotene and Fucoxanthin( brown coloured Xanthophyll).  They lack chlorophyll-‘b’ and billiproteins.

7.      The reproduction takes place by vegetative, asexual and sexual methods. The diploid zygote directly germinates into sporophytic plant body without zygotic meosis. Hence the plant body is sporophyte and gametophyte only during meiosis.

3.Rhodophyceae:

           

            Characteristics of Rhodophyceae:

1.      The red algae are found in marine water their number is high in deeper and warmer parts of subtropical and tropical water but their number is less in polar seas. Few fresh water species such as Bactrachospermium, Lamanea, Thorea are found in cold and fre flowing water. Their number is high in marine water. Unicellular red algae like Porphyridium is found in terrestrial habitat. Some red algae like Polyciphonia, Calceocolax are in Parasitic form of Rhodophyceae.

2.      Habit: Except few unicellular form like porphyridium palmelloid form like Asterocytic,Filamentous form like Goniotrichum most of the red algae are categorized in to two types on the basis of their thallus organization.they are:

-Uniaxial(one axis) form: Bactrachospermum, Dumontia,Delesseria

-Multiaxial(many axis and each axis giving many branches) :Polysiphonia,Helminthocladia, chondrus

3.       Cell wall is double layered, inner-layer is made up of cellulose and outer layer contains pectic material along with polysulphated esters such as agar,porphyrans.

4.      The reserved food materials are FLoridean starch(complex carbohydrates),florodoside,mannoglycerate and fat droplets.

5.      Rhodophyceae reproduces by vegetative,asexual and sexual methods

-vegetative by fragments in some cases

-non-motile sspores help in asexual which is Peculiar character

-sexual method by progamous.

6.      The pigments in Rhodophyceae are

-chlorophyll-‘a’ (C₅₅H₇₂O₅N₄Mg)

-chlorophyll-‘b’ (C₅₅H₇₀O₆N₄Mg)

-Carotenes

-xanthophylls

-r-phycocyanin

-r-phycoerythrin

In bottom the light energy of sun cannot reach only blue and violet rays could reach which are trapped by the phycobillins and transferred to chlorophyll. They occur red at bottom when brought surface they occurs white in colour.