ALGAL CELL STRUCTURE
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.
0 comments:
Post a Comment