Because they sometimes do not properly fit in one of the kingdoms since they may have characteristics from a few of the kingdoms.
Classification of Viruses. Viruses are not usually classified into conventional taxonomic groups but are usually grouped according to such properties as size, the type of nucleic acid they contain, the structure of the capsid and the number of protein subunits in it, host species, and immunological characteristics. Caliciviridae, Picornaviridae, Reoviridae. Genera have the suffix-virus. Within the Picornaviridae there are 5 genera: enterovirus, cardiovirus, rhinovirus, apthovirus and hepatovirus. The definition of ` species ' is the most important but difficult assignment to make with viruses. An important part of the scheme proposed by Lwoff and colleagues is that viruses are grouped according to their properties, not the cells they infect. The nucleic acid genome was also recognized as a primary criterion for classification.  They both contain genetic material (RNA OR DNA), and they both reproduce. A virus is a small infectious agent that can replicate only inside the living cells of other organis … ms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Viruses do not behave like other living cells. For one, they can only reproduce within other organisms. And essentially that is about all they do. Granted there are negative r … eprocussions for the host organism, but the virus itself simply multiplies. Virus classification is the process of naming viruses and placing them into a taxonomic system. Similar to the classification systems used for cellular organisms, virus classification is the subject of ongoing debate and proposals. This is mainly due to the pseudo-living nature of viruses, which is to say they are non-living particles with some chemical characteristics similar to those of life. As such, they do not fit neatly into the established biological classification system in place for cellular organisms. Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause 1. Virus classification is the process of naming viruses and placing them in a 'family tree' in relation to other viruses. This process is different from the one used to classify plants or animals. Thanks to the fossil record, there are clear connections between most animals or plants. Viruses do not leave such a record, so it is more difficult to determine relationships between them. There are other classification systems that are based on the morphology of the virus or the disease caused. These systems are inadequate due to the fact that some diseases are caused by different viruses, the cold or flu are the most common example of this and some viruses look very similar to one another. The nucleus (or lack thereof) and the cell wall. Explain, using the traditional definition of species, why it is difficult to classify some bacteria and archaea at the species level. A species can be defined as an interbreeding group of organisms that produce fertile offspring.  Viruses are similar to living organisms because both contain  hereditary material (RNA or DNA), and both reproduce. Viruses are  different from living organisms because they … do not use energy to  grow, and do not use energy to respond to their surroundings. Viruses do not behave like other living cells. For one, they can only reproduce within other organisms. And essentially that is about all they do. Granted there are negative r … eprocussions for the host organism, but the virus itself simply multiplies. The ICTV classifies RNA viruses as those that belong to Group III, Group IV or Group V of the Baltimore classification system of classifying viruses and does not consider viruses with DNA intermediates in their life cycle as RNA viruses. Viruses with RNA as their genetic material but that include DNA intermediates in their replication cycle are called retroviruses, and comprise Group VI of the Baltimore classification. Notable human retroviruses include HIV-1 and HIV-2, the cause of the disease AIDS. We must r … ely on the ability of our immune systems to render the virus particles inert/inactive by blocking their entry into our cells with antibodies, or rely on vaccines to prevent the viral infections. In addition, it is difficult to prevent infections by viruses that easily mutate, such as the common cold. They mutate so rapidly and into so many different forms it is not possible to create a vaccine before the virus has mutated again. This is also one of the reasons why we need an annual vaccination for the flu. Some algae are difficult to classify because they sometimes do not properly fit in one of the kingdoms since they may have characteristics from a few of the kingdoms. It is difficult to classify viruses as living organisms because they are not made of cells. They only become alive when they find a host i.e. a living cell to live in. Some algae are difficult to classify because they sometimes do not properly fit in one of the kingdoms since they may have characteristics from a few of the kingdoms.
http://www.nlv.ch/Virologytutorials/Classification.htm http://www.virology.ws/2009/08/07/how-viruses-are-classified/ http://www.answers.com/Q/Why_viruses_are_difficult_to_classify_as_living_organisms https://en.wikipedia.org/wiki/Virus_classification http://ezinearticles.com/?Virus-Classification&id=251837 http://images.pcmac.org/SiSFiles/Schools/GA/VidaliaCity/VidaliaHigh/Uploads/Presentations/CLASSIFICATION.pptx http://www.answers.com/Q/Why_viruses_are_difficult_to_classify_as_living_organisms https://en.wikipedia.org/wiki/RNA_virus http://www.answers.com/Q/Why_is_it_difficult_to_classify_viruses http://www.answers.com/Q/Why_is_it_difficult_to_classify_viruses
why are viruses such a difficult group to classify