#1 Why aren’t Viruses “alive.”
According to the seven characteristics of life, all living organisms must grow, reproduce, respond to stimuli, evolve, respire, excrete and have a highly complex organized structure. Biologists use some of these characteristics to determine whether something is living or non-living. Let’s look at some of these traits and how they compare with those of viruses to better understand why viruses are not living organisms.
Living organisms reproduce by passing on genetic information dissimilar to viruses which replicate after hijacking the host’s cells. The continuity of life occurs because organisms reproduce themselves using a molecular blueprint called DNA. Unlike living organisms, viruses can neither grow nor reproduce independently since they do not have the compound cellular organelles that this activity requires. It requires the help of another living organism to replicate. 29
For a virus to survive and multiply, it needs all three things: a host cell with some of its own genetic material; another living organism (usually bacteria) that will serve as a "vector"; and finally, one or more basic tryptophan molecules that makeup part of the genome. When they infect a cell, they use the host’s DNA to replicate their own genetic material and then use the host’s machinery to make new virus particles. Since they have no cell membranes or organelles, viruses are not considered living organisms.
Moreover, compared to living organisms with cell membranes and other organelles such as ribosomes and mitochondria sites for protein synthesis and respiration, viruses have no membranes; they consist of either DNA or RNA molecules surrounded by a protein layer. They also have no ribosomes to make protein, no cytoplasm, and no energy source because they have no mitochondria.
Living things react to changes in their environment. Organisms react to internal and external environmental fluctuations since they have sensory apparatus that allows them to respond to illumination, sound, chemicals, and many other influences from the surrounding, unlike viruses which only interact with the cells they invade based on the virus’ chemical makeup and the environment in which it ends up. From the comparisons above, one can conclude that the simplicity and characteristics of viruses make it impractical to term them as living, making it impossible to classify them as living organisms. 29