| Talk in general about bacteria | Bacteria are considered as the most ancient living forms on earth. They can colonize many environments even the harshest ones. They are divided into Eubacteria and Archaebacteria. Bacteria are prokaryotes; they are unicellular organisms that lack membrane-bound organelles and a defined nucleus. |
| How is the mode of reproduction of bacteria? | Bacteria are organisms which reproduce through asexual reproduction; they are not able to reproduce by mitosis or meiosis because they lack a true nuclei.
They do not have different sexes, and they are capable of “splitting” themselves into two or more individuals. |
| Talk about binary fission of bacteria. | Most bacteria reproduce by a process called binary fission or scissiparity. Binary fission is basically an asexual mode of cell division where a single parent bacterial cell replicates its DNA before splitting into two new daughter cells.
Under ideal conditions, bacteria divide (reproduce) rapidly, doubling their numbers every 20 minutes. |
| Talk about endospores of bacteria. | Several types of bacteria are able to form resistant spores when the conditions are hostile. Endospores are spores formed within the cell wall of a parent cell. Endospores are resistant resting cells, protected by several thick layers.
The spore will remain dormant for a period of time before it can be induced to germinate and to revive the vegetative state in hospitable environments. |
| Talk in general about asexual reproduction of cyanobacteria. | All cyanobacteria are unicellular, though many grow in colonies or filaments (trichomes), often surrounded by a gelatinous or mucilaginous sheath.
Cyanobacteria present several forms of asexual reproduction: - Unicellular cyanobacterial cells divide and reproduce by binary fission and spore formation.
- Filaments may fragment, often at weak points where a cell has collapsed (hormogonia) or near a nitrogen-fixing site (heterocysts). |
| Talk about hormogonia. | Filamentous cyanobacteria reproduce by fragmentation of their filaments (trichomes) at more or less regular intervals to form short pieces of filaments. These pieces of filaments (surrounded by a mucilaginous sheath) are called hormogonia. The latter show gliding motility and develop into new filaments. |
| Talk about heterocysts. | Within the filament, heterocysts are specialized enlarged thick cell wall that fix nitrogen. When environmental conditions trigger reproduction, certain heterocysts in the filament die causing the defragmentation of the trichome into multicellular fragments. Each fragment is capable of growing into a new filament. |
| Talk about akinetes. | Under unfavorable conditions, some Cyanobacteria form resistant spores called akinetes - enlarged vegetative cells with a thickened outer wall. Akinetes are dormant cells. They are resistant to cold and drought (desiccation). They also accumulate and store various essential materials, thus allow the Cyanobacteria to survive under unfavorable environmental conditions. Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell. |
