Is a Virus a living thing?
Are viruses alive or not? To figure out this question we first have to know, what defines a living thing. According to the online Merriam-Webster Dictionary, life is in particular “an organismic state characterized by capacity for metabolism, growth, reaction to stimuli, and reproduction.” For about 100 years, scientists have repeatedly changed their mind over what viruses are. First seen as poisons, then as life-forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving: they cannot replicate on their own but can do so in truly living cells and can also affect the behavior of their hosts profoundly. Viruses, like bacteria, are microscopic and cause human diseases. But unlike bacteria, viruses are acellular particles (meaning they aren't made up of living cells like plants and animals are), consisting instead of a central core of either DNA or RNA surrounded by a coat of protein. Furthermore they also lack the properties of living things: They have no energy metabolism, they do not grow, they produce no waste products, and they do not respond to stimuli. Therefore one of the fundamental marks of life is the ability to reproduce. Some argue that since viruses cannot reproduce independently, they are not alive. However, similar to viruses, there are a few prokaryotes that are parasites and cannot reproduce without a host. But these prokaryotes show another hallmark of life that viruses lack: growth. Once assembled, a virus does not change in size or chemical composition. They lack the machinery for producing energy to drive such biological processes. This makes them radically different from any known organism. Viruses do, however, show some characteristics of living things. They are made of proteins and glycoproteins like cells are. They contain genetic information needed to produce more viruses in the form of DNA or RNA, like mentioned before. They evolve to adapt to their...
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