General characters of cyanophyceae algae notes | bizbotany

 General characters of Cyanophyceae notes

Some important distinguishing features of blue-green algae are as follows:

1. They are unicellular(e.,g chrococcus). colonial (e.,g., Gloeocapsa) or form chains of cells- trichomes (e.g., Oscillatoria). In colonial forms, all cells of a colony occur in a common gelatinous matrix. The cells of the colony may divide to form definite(e.g., Merismopedia) or indefinite and irregular( i.e., Aphanotheca) assemblage of cells. In filamentous forms( a trichome surrounded by a sheath is called a filament), each trichome has its own gelatinous sheath. The filaments are usually un branched and uniseriate( e.g., Nostoc) or may sometimes show psuedo-branching.
2. Their cell structure is prokaryotic. They lack membrane bound organelles and the nucleus is of incipient type.
3. The cell wall is composed of microfibrils held together in a mucilage sheath. The orientation of fibres may be reticulate or long intertwining parallel. It helps in sloughing off parasites and in retaining water, thus avoiding dessication.
4. The cell wall is differentiated into four layers. It is composed of mucopeptide, together with carbohydrates, amino acids and fatty acids.
5. The principal pigments are chlorophyll a , c-phycocyanin and c-phycoerythrin. and they impart characteristic blue green color to these algae.
6. They lack membrane bound plastids. Instead, pigments are found embedded within lamellae composed of two membranes joined at the ends. These structures are known as thylakoids.
7. They show gliding or jerky movements; flagella being altogether absent.
8. The reserve food material is a special type of starch and protein.
9. In some blue green algae specialized structure known as heterocysts are present. They may be terminal or intercalary in position. Definite function of heterocyst is not known, but they are supposed to be the center of nitrogen fixation.
10. Reproduction takes place by vegetative and asexual methods. Sex organs, gametes and flagellated zoospores are altogether absent. However, in some genetic recombination has been reported.
11. Vegetative reproduction takes place by cell division, fragmentation and hormogonia formation.
12. Asexual reproduction takes place by akinets, endospores, exospores, heterocysts and nannocytes.