Are viruses alive?
The question about defining viruses as living organisms or not is a question that has been around for some time and continues to be debated by biologists. To a very real extent, the answer depends on how you define what life is. Many people use a set of criteria to define life and most include the criterion that life includes the ability to reproduce. Viruses cannot reproduce on their own. They must use the cells of a host organism in order to replicate their viral DNA and produce a new virus. While many parasitic organisms use a host to facilitate their life processes, a virus has to use the actual cell replication machinery to replicate its DNA. So unlike a parasite which uses the host as a source of food and energy to replicate, the virus cannot replicate on its own without using the host cell. So if you use the ability to self-reproduce as a criterion for life, depending on how you interpret it will depend on your view if viruses are alive or not. It really is a personal judgement call.
This is a question that is debated by many. Viruses are the fine line between living and non-living matter. When a virus is not attached to a host cell it is inactive, in this form it is easy to say that a virus is not alive. However when a virus attaches itself to a host cell it is going to do one of two things; use the cells reproductive "machinery" to make copies of itself or insert itself into the host cells DNA. When a virus uses a host cell's reproductive "machinery" so to speak it makes copies and then it will leave the cell one of a couple different ways killing the host cell. If it inserts itself into the DNA's genetic material then it will stay there until a time when the conditions are better and then reproduce itself. It can be argued that doing these things means a virus is alive, or shows at least some properties of life making this a difficult question to simply say yes or no too!