Viewpoint #1 - The word “virus” has its origins in the Latin term for “poison.” In the late 19th century, scientists discovered
agents that behaved like bacteria causing diseases such as rabies and hoof-and-mouth, but were much smaller. Like bacteria, viruses contain one of the two nucleic acids: DNA or RNA. The scientists noticed that these particles could be spread from one person to another, with serious consequences: illness and death. At this time it became the general view that viruses were biologically "alive," the simplest of all life on Earth. An important characteristic of life is the response to stimuli. Scientists noted that viruses may exist in two distinct states. When they are not in contact with a host cell, the virus remains dormant. Today, this is called the lysogenic cycle. During this time there are no biological activities occurring and the virus is really just a particle. Viruses can remain in this dormant, non-living state for extended periods of time, waiting to come into contact with a host cell. When the virus comes into contact with the host, it becomes active, reacts to its environment and/or host and directs all its energy toward reproduction. This cycle is referred to as the lytic cycle. The viral goal now is to produce more viruses that then attack more host cells.
Viewpoint #2 - In 1935 scientists discovered and crystalized the virus responsible for the tobacco mosaic virus. They discovered that viruses consisted of a nucleic acid, either DNA or RNA, surrounded by a protein shell. Once again, the scientific view changed: viruses may be complex biochemical particles but they are not alive.
Viruses depend on the host cell for the raw materials and energy necessary for nucleic acid and protein synthesis, as well as all other biochemical activities that allow the virus to multiply and spread. Most simple life forms use cell division to reproduce, while viruses spontaneously assemble within cells. They concluded that even though reproduction occurs under viral direction, viruses are simply nonliving parasites of other life forms.
The simple question of whether or not viruses are alive, has defied a simple answer because it raises the fundamental issue: What defines life?
Viral Replication
Consider the debate about whether viruses are alive or not. Both Viewpoint #1 and Viewpoint #2 have points of evidence in common. That includes ALL BUT
A) viruses are pathogens.
B) viruses require a host cell.
C) viruses undergo cell division.
D) viruses contain a nucleic acid.
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50-70%. At the age of 1, percentage is around 65%. In adult men, 60% of their bodies is water. 55% of adult women's weight is water due to fat not holding as much water as lean tissue; fat makes up more of women's bodies than men.
