Viruses and Major Groups of Living Things | Biology Form 1 Topic
There are many species of living organisms in the world. These organisms are placed in groups based on their common or shared characteristics. Each group has its own features that make it distinct from others. Viruses A virus is an extremely small fragment of nucleic acid (DNA or RNA) surrounded by a protein coat. It is smaller than a living cell. A virus is not a cell. Different types of viruses (a) Tobacco mosaic virus (b) Bacteriophage virus (c) Influenza virus Characteristics of viruses (a) They do not have a nucleus, cytoplasm, or cell organelle. (b) They have a simple structure consisting of a small piece of nucleic acid (DNA or RNA) surrounded by a protein coat called a capsid. Some viruses have viral envelopes. These are membranes enclosing capsids. The envelopes are made up of proteins from the host cell. (c) They cannot reproduce on their own. They must attack a host cell and use the materials in the cell to reproduce. This is called obligate parasitism. Obligate parasitism i...
