Viruses are obligate, intracellular parasites - they are completely dependent on cells as hosts. Viruses can only replicate inside a cell and once inside a cell take over the cell's biosynthetic machinery. The abundance and diversity of viruses is immense and those that infect bacteria (bacteriophages) are important in regulating their numbers.  Viruses are very small (nanometers in size) but do vary in shape. However, viruese do fall into two general categories, a) those enclosed by shell of protein called a capsid and b) those enclosed by a capsid and membrane-like envelope.

The image below is an example of a bacteriophage.



The image below is an example of a spherical insect virus.

Insect virus

Last Modified: Wed, 21 Jun 2017 11:26:29 SAST