ALGAL CELL STRUCTURE

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There is a great diversity in the thallus structure in algae. They vary from tiny single-celled species one micrometer in diameter to giant seaweeds over 50 meters long. Broadly, all algae may be divided into two types regarding their structure. There are two types of algae regarding their structure – Unicellular algae and multicellular algae
1. UNICELLULAR ALGAE:- The unicellular algae are all sizes and shapes. They range from small spherical cells to large irregular shaped cells. The unicellular forms may be spherical, oblong, pear-shaped or sometimes elongated bearing flagella (Chlamydomonas, Euglena) etc. These are of following two types –
(a) Non-motile:- Non-motile unicells, without flagella. Many unicellular algae do not possess any outgrowth for locomotion, e.g., Chlorella
          (b) Motile:- Motile unicells, with flagella. Many unicellular motile forms may be spherical, oblong, pear-shaped or sometimes elongated and bears flagella for locomotion, eg., Chlamydomonas, Euglena, etc.
2. MULTICELLULAR ALGAE:- Multicellular algae are of more diverse forms. They may remain in the form of colony or may be filamentous forms. These are as follows –
(a) Non-motile Colony:- Number of cells in these colonies is indefinite and they are non motile (Hydrodictyon, Pediastrum).
(b) Motile Colony:- In these algae, definite number of cells are found and these are motile, such as Scenedesmus, Gonium (small colony), Volvox (big colony).
(c) Amorphous Colony:- They are also called as Palmelloid forms. Algae cells in this type are surrounded by a viscous mucilalginous substance (Microcystis, Tetraspora).
(d) Dendroid colony:- Cells of these forms produce mucilaginous substance and are folded in such a manner that they look like branches of a plant, e.g. Dinobryon.
(e) Filamentous:- Filamentous algae (floating or attached). The simplest filamentous algae consist of a thallus, of a single chain of cells. This is the result of cell division in one plane only. The filaments may be unbrached filamentous forms. Such types of thalli are found in many algae and consist of a straight row of cells (Spirogyra, Ulothrix, Oedogonium).
(i) Simple Unbranched filaments, e.g., Ulothrix
(ii) Simple branched filaments, e.g., Cladophora
(iii) Psuedo-branched filaments, e.g., Scytonema, Ulothrix
(iv) Heterotrichous forms (heteros =different): Some cells in the filaments divide several times in different planes resulting in two parts. Thallus consists of two parts, i.e. horizontally running main trichome and a vertical erect trichome e.g., Draparnaldiopsis, Chara
(f) Siphonous or Siphonaceous:- The thallus undergoes repeated nuclear division without the accompanying formation of cell walls. As a result tubular structure with the multinuclear cytoplasm lining is formed known as coenocytic as in siphonales e.g., Vaucheria, Caulerpa.
(g) Parenchymatous:- Seaweeds made up of "boxy" cells like those of higher plants are termed parenchymatous. They may be membranous like Ulva, the sea lettuce. In these algae, cell division takes place on different sides with the result that they become parenchymatous, e.g., Ulva, Macrocystis.
            (h) Psuedoparenchymatous:- Psuedoparenchymatous algae have thalli that superficially resemble parenchyma, but which are actually composed of appressed filaments or amorphous cell aggregates. e.g., Monostroma.
Prema Iswary,               
Assistant Professor,     
Department of Botany.
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