Ulothrix
systematic position
Kingdom - Plantae
Subkingdom - Thallophyta
Phylum - Chlorophyta
Class - Chlorophyceae
Order - Ulotrichales
Suborder - Ulotrichineae
Family - Ulotrichaceae
Genus - Ulothrix
Ulothrix is a genus of non - branching filamentous green algae generally found in fresh and marine water. Its cells are normally as broad as they are long and they thrive in the low temperatures of spring and winter . They become attached to surfaces by a modified holdfast cell.
Structure of Ulothrix
*Plants belonging to Thallophyta do not have a well differentiated body.
*The plant body consists of unbranched , uniseriate filament.
*The apical cell is somewhat rounded at its terminal end whereas the basal holdfast, which attaches the filament to the substratum.
*The cell wall is composed of propection and cellulose and it lacks mucilage.
*Each cell has a single girdle-like and perital chloroplast and two to many pyrenoids are present in each chloroplast.
*Each cell contains a distinct nucleus, a central vacuole, and a large thin chloroplast.
The plant body is differentiated into three regions .
1.Basal cell
2.Apical cell
3.Middle cell
1.Basal cell
It is the lowermost cell of the filament,commonly long, gradually narrowed downwardly and towards the basal end it expands and forms a dise-shaped structure. The cell is hyaline or brownish in colour , which performs the function of fixation to the substratum and called holdfast
2.Apical cell
It is the topmost cell of the filament, which is dome- shaped and green in colour. The topmost cell of the filament, which is dome- shaped and green in colour.
3.Middle cell
All the cells in between basal and apical cells are alike. The cells are broader then its length i.e rectangular in shape .
Repoduction in Ulothrix
Reproduction in ulothrix taes place by means of vegetative ,accidental breaking of the filament a sexual and sexual.
1.Vegetative reproduction
The common vegetive methods of reproduction are fragmentation and akinete formation .
Fragmentation
Vegetative cells of Ulothrix break into small pieces accidentally. Each fragment develops into a new filament.
2.Asexual Reproduction
Asexual reproduction takes place in winter, during its active growth. It takes place by the formation of zoospores , akinetes and palmella stage.
a.Akinete formation
Some of the vegetative cells of Ulothrix are converted into thick walled akinetes. Foodreserves are accumulated within the akinetes. When the conditions are favourable each akinete develoops into a new plant.
b.Zoospore formation
zoospore are formed during favourable condition with proper growth of the plant. Any cell except holdfast is capable of producing zoospore formation the protoplast becomes slightly contracted from the cell wall.
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The zoospores are of different types ,
Type of Zoospores :
Species of Ulothrix with narrow cells produce quadriflagellate zoospores of one kind. But species with broader cells like U.zonata produces 3 type of zoospores.
These are:
*Quadriflagellate macrozoospores usually 4 per cell.
*Quadriflagellate microzoospores usually 8 per cell.
*Biflagellate micro-zoospores usually 16-32 percell.
Germination of zoospores:
After maturation the zoospores are liberated throught a pore developed on the side wall and initially remain in a delicate mucilage vesicle. The vesicle soon dissolves and zoospores are liberated . The zoospores can swim for different period of time (few hours to even 6 days ).
Coming in contact with suitable substratum they lose their flagella and get attached. The cell divides horizontally. They lower attached cell develops into holdfast and the upper cell forms the filament through repeated divisions.
c. Aplanospores:
With the sudden change unfavourable condition during zoospore formation the protoplast units do not form flagella and remain inside the mother cell as non-motile units. These unicellular, uninucleate, thin walled non-motile units are called aplanospores. During favourable condition they germinate after or before liberation from parent cell.
d.Hypnospores:
During drought, sometimes the entire protoplast of a cell may round up and forms a single thick walled structure, the hypnospore. During favourable condition it germinates and develops into a new filament.
e.Akinetes:
Akinetes are formed during extreme unfavourable condition. During favourable condition it germinates and develops into a new filament.
f.Palmella stage:
Sometimes the wall of the aplanospore mother cell becomes mucilaginous.Consequently the wall of aplanospores also gets enveloped by mucilaginous substance. These covering protect the aplanospores against desiccation.
In this way many green round bodies become enclosed in a mucilaginous mass,called palmella stage.During favourable condition these green bodies come out by the dissolution of the mucilage covering and germinate into new plants.
3.Sexual Reproduction:
Towards the end of growing season they reproduce by sexual season they reproduction by is isogamous i.e,the union between similar gametes.
The fusion takes place between the gametes developed in different filament i.e they are heterothallic or dioecious(U.rorida is monoecious).Morphologically gametes are similar to the microzoospores.They are produced in the gametangium similar to zoosporangium.
Depending on species the number of gametes may be 8,16,32,or64.Like microzoospores they are uninucleate and biflagellate but smaller in size.
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