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→Concept Bacteria
3) '''Structure of Bacteria :'''<br>
3) '''Structure of Bacteria :'''<br>
Structure of Bacterial Cell<br>
Structure of Bacterial Cell<br>
Bacterial is very small, simple unicellular organisms with a length varying from 2 to 5. <br>On the basis of shape bacteria are either coccus (spherical), bacillus (rod shape), spirillum (spiral) or vibro (comma) types. <br>On the basis of arrangement of flagella, these may be atrichous (flagellum absent) <br>monotrichous (one flagellum at one end), leptotrichous (bunch of flagella on one side), amphitrichous (flagella on whole surface).
Bacterial is very small, simple unicellular organisms with a length varying from 2 to 5. <br>On the basis of shape bacteria are either coccus (spherical), bacillus (rod shape), spirillum (spiral) or vibro (comma) types. <br>On the basis of arrangement of flagella, these may be atrichous (flagellum absent) <br>monotrichous (one flagellum at one end), leptotrichous (bunch of flagella on one side), amphitrichous (flagella on whole surface).<br>
Internal structure:<br>
[[File:Structure of Bacteria.jpg|400px|left]]<br>'''Cell wall''':
Bacterial cell is surrounded by a prominent cell wall constituted by polysaccharides, lipids and proteins. <br>The cell wall is permeable to water and ions of small molecules.<br>
'''Slime layer and capsule''':<br>
Some bacterial cells are completely enveloped by a slimy layer, which is relatively thick to form the capsule. Capsulated bacteria are more harmful. Capsule protects the cell from antibodies and desiccation.<br>
'''Mesosomes''':<br>
Mesosomes take part in aerobic respiration and it is found in gram positive bacteria. The protoplasm is either transparent or granular.<br>
'''Protoplasm''':<br>
Below the cell wall, the plasma membrane is present. Plasma membrane at certain points forms coiled invaginations called Mesosomes.<br>
'''Cytoplasm:'''<br>
Cytoplasm is composed of complex proteins, lipids and mineral, nucleic acid and water. <br>Glycogen is the reserve food material. It contains 70S type of ribosomes. <br>Other organelles like endoplasmic reticulum, mitochondria; Golgi complex, etc. are absent. <br>However, in photosynthetic bacteria some pigments are present (bacterio chlorophyll).<br>
'''Nucleoid''':<br>
Bacteria are prokaryotes, there is no well-organised nucleus. Nuclear membrane and nucleolus are absent. <br>At the center there is a clear zone called nucleoid where only a single naked chromosome (without histone protein, only DNA)<br> is present in a very much coiled form.<br>
'''Episomes'''<br>
In addition to the DNA in some bacterial cells an additional circular DNA is present in the cytoplasm. It is called as episome or plasmid.<br>
===Learning objectives===
===Learning objectives===
