Deoxyribonucleic acid or DNA is the nucleic acid, containing the sugar deoxyribose, which forms the materials of which the chromosomes and genes of organisms are composed. It carries the blueprint for construction of all the cells of an organism and all instructions that control their activities, and which enables these instructions to be passed on from one generation to the next. DNA is found in all living organisms except certain viruses which contain RNA (ribonucleic acid), a closely related nucleic acid.
Tuesday, May 31, 2011
Tuesday, May 3, 2011
Every different kind of organism called a species, and closely related species are grouped together into genera (the singular of with is genus). Each species has a two part scientific name, composed of its generic name and its species name. For example, the house fly, which belongs to the genus Musca, is scientifically known as Musca domestica. Where a number of members of the genus Musca are mentioned, later examples may be abbreviated to, for instance, M. domestica. By convention the genus name begins with a capital letter.
Related genera are grouped into families, related families are grouped into Orders, Orders are grouped into classes, and classes are grouped into phyla. The latter are the largest divisions of each kingdom. Family names in the animal kingdom always end in …idea, while plant families always end in ..aceae.
Monday, May 2, 2011
Viruses are on the borderline of living and non living things and do not fit into the five kingdoms of the living world. They are much smaller than bacteria and each consists simply of a lump of DNA inside a protein envelope.
There are many different kinds of viruses and they all produce disease in plants and animals by invading living cells and interfering with their normal functions. The viruses can be converted to a crystalline form, in which they can survive for a very long time, but they cannot grow or reproduce on their own. They need the help of the host cells for this. The virus DNA takes control of the cell nucleus and instructs it to make more virus mater. The new virus particles then escape from the host cell and rapidly infect other cells. Human diseases caused by viruses include the common cold, measles, polio and aids