VIRUSES

VIRUSES

When the five-kingdom system of classification was devised, on one was able to find a place for the group of organisms called the viruses. This is because viruses do not show the typical features of living things - respiration, nutrition and reproduction, for example - unless they are inside the cells of another living organism. In other words, all viruses are parasites and therefore cause harm to their host. Some taxonomists have suggested that viruses belong in a sixth kingdom. There is great variation in the structure of viruses, but they all have certain common features.
Most viruses cause disease - they may infect humans, domestic animals or plants.
It is important not to confuse viruses with bacteria. The structure of bacteria and theis importance to humans are described .
The pages that follow describe the characteristics that distinguish. Living organisms in some of the most important phyla and classes.