Question

Give a brief account of chlorophyceae class of algae with the help of diagram.long question​

Answer 1

Answer:

The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example, the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales. They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral or ribbon shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some algae may store food in the form of oil droplets. Green algae usually have a rigid cell wall made up of an inner layer of cellulose and outer layer of pectose.

Chlorophyceae

Pediastrum.jpg

Scientific classificatione

Phylum:

Chlorophyta

Class:

Chlorophyceae

Wille in Warming, 1884[1]

Orders[2]

Chaetopeltidales

Chaetophorales

Chlamydomonadales

(= Volvocales)

Chlorococcales

Oedogoniales

Phaeophilales

Sphaeropleales

Tetrasporales

Answer 2

$\rightarrow$ Chlorophyceae (chloros, green; phyceae, algal organisation) is commonly known as green algae’. Fritsch (1935) considered to include the green algae under the class Chlorophyceae, which have been raised to the rank of division Chlorophyta by Smith (1938), Tippo (1942) and Bold (1950).

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$\rightarrow$ Later Prescott (1969) and Round (1973) considered it to the rank of phylum Chlorophyta. Papenfuss (1946) included the suffix ‘phyco’ to the divisions of algae and named chlorophyta as Chlorophycophyta. Later Bold and Wynne (1978) also followed the same suggestion. Considering more appropriate, the classification of Fritsch (1935) is followed in this book.

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$\rightarrow$ This class consists of 425 genera and about 6,500 species but, later Prescott (1969) reported that the number of species may be as many as 20,000; with more being discovered continuously. The name green alga is given because of the presence of domi­nant pigments like Chlorophylls a and b over the carotenoids and xanthophylls. They are all eukaryotes.

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$\large\bold{Occurrence\:of\:Chlorophyceae}$

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$\rightarrow$ The members of Chlorophyceae generally grow in fresh water (about 90%) and the rest in saline water, terrestrial habitat etc. The fresh water members such as Volvox, Oedogonium, Spirogyra etc. grow in ponds, pools and lakes.

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$\rightarrow$ Members of conjugales (e.g., Spirogyra, Zygnema etc.) and Oedogoniales (e.g., Oedogonium etc.) are strictly fresh water, but the members of Ulvaceae and Siphonales are pre­dominantly marine. Some members of Volvocales, Chaetophorales and Cladophorales grow both in fresh and saline water.

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$\rightarrow$ Some species of Ulothrix and Vaucheria are subaerial and grow on damp soil. Some members may be terrestrial and grow as epiphytes on tree trunk, leaves etc. (e.g., Trentepohlia); as epizoic i.e., (growing on animal bodies (species of Characium and Cladophora); as endophytes (e.g., Chlorella), as parasites (e.g., Cephaleuros, Rhodochytrium and Phyllosiphon) and also cause diseases.

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$\rightarrow$ They can also grow in further different habitats like hot springs (Chlorella), snow (Chlamydomonas yellowstonensis), saline water (C. ehrenbergi) and some remain as partners in lichen associations.

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$\large\bold{Important\:Characteristics\:of\:Chlorophyceae}$

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$\rightarrow$ Members of Chlorophyceae grow mostly in fresh water, a few in brackish and saline water and a few are terrestrial.

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$\rightarrow$ They show wide range of variations in their thallus structures like unicellular motile (Chlamydomonas) and non-motile (Chlorella), coenobium (Volvox), palmelloid (Tetraspora), dendroid (Ecballocystis), fila­mentous branched (Cladophora) and unbranched (Spirogyra), heterotrichous (Coleochaete), siphonaceous (Vaucheria) and parenchymatous (Ulva).

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$\rightarrow$ Flagella are 1-many, equal in size and inserted either apically or sub-apically. The flagella show typical 9+2 arrangement when viewed under E.M.

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$\rightarrow$ The cells are eukaryotic in nature. Usually there is only one nucleus in each cell, but in Siphonales and Cladophorales many nuclei are present in their coenocytic body. Normally the number of nucleolus is one per nucleus, but several nucleoli are present in the members of Conjugales.

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$\rightarrow$ The cell wall is mainly made up of cellulose, which comprised of hydroxyproline glyco­sides or xylans and mannans. In Chara the cell wall is encrusted with calcium and magnesium carbonate.

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$\rightarrow$ Inner to the cell wall, semipermeable cell membrane is present which encircles the protoplast. The cytoplasm contains many small vacuoles which pushes the nucleus with cytoplasm towards the periphery and called primordial utricle.The cells are eukaryotic in nature. Usually there is only one nucleus in each cell, but in Siphonales and Cladophorales many nuclei are present in their coenocytic body. Normally the number of nucleolus is one per nucleus, but several nucleoli are present in the members of Conjugales.

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$\rightarrow$ The flagellate cells have eye-spot or stigma in the anterior portion, which remain inser­ted at one side of the chloroplast.

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$\rightarrow$ The pigments are located in the chloro­plast. Chkiroplast generally contains pyrenoid(s).