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A very small infectious agent that can reproduce only inside other cells.
A very small infectious agent that can only reproduce inside other cells. Viruses have a very simple structure: just a packet of nucleic acid in a protective protein shell, sometimes with an outer phospholipid membrane. Opinions are divided on whether viruses are living organisms or not. They have genes and evolve by natural selection, but they cannot survive outside living cells, have no cellular structure of their own, and do not have their own metabolism.
Viruses have a very simple structure: just a packet of nucleic acid in a protective protein shell, sometimes with an outer phospholipid membrane. Opinions are divided on whether viruses are living organisms or not. They have genes and evolve by natural selection, but they cannot survive outside living cells, have no cellular structure of their own, and do not have their own metabolism.