What is Cyanobacteria ? Give the characteristic features of it.

Ans. Cyanobacteria are blue-green algae bacteria. They are prokaryotic and their nuclear material is deoxyribonucleic acid (DNA) which is present in the protoplasm in dispersed form without any nuclear membrane throughout the cell. The membrane bounded plastids and large vacuoles are absent from the cell of cyanobacteria. The cell walls of cyanobacterial show some chemical similarity to those of bacteria. Certain cyanobacteria may be infected with viruses which resemble bacteriophages which also show similarity between cyanobacteria and bacteria.

Characteristic features: The important characteristic features of Cyanobacteria are as follows:

1. They are present everywhere and occur in all possible kinds of habitats.

2. The flagella are absent.

3. The storage products are cyanophycean starch and proteins.

4. They may be unicellular (e.g. Chlorococcum, Gloeocapsa, Tetrapedia colonial (e.g. Aphanocapsa, Nostoc) and filamentous (e.g. Oscillatoria).

5. The filaments are called trichomes which are generally surrounded by a sheath.

6. Some cyanobacteria live in symbiotic association with other organisms.

7. Many members have the ability to fix atmospheric nitrogen in the soil.

8. They form a thick stratum on the surface of saline usar soils during rainy season.

9. In many cases thick walled heterocysts are formed.

10. In some filamentous forms akinetes are formed due to the accumulation of much food.

11. They may reproduce asexually by endospore (e.g. Dermocarpa) and exospores (e.g. Chamaesiphon).

12. The trichomes of oscillatoria show oscillating movement. In some cases the trichomes movement is called gliding movement.

13. Some cyanobacteria live in symbiotic association with protozoan and are called Cyanellae.

The common examples of Cyanobacteria are Nostoc, Oscillatoria, Anabaena, Gloeocapsa, Chlorococcus, Cylindrospermum, Gloeotrichia, Rivularia and several others.

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