They are not a living so they are not related to cell theory. In more words Cell are structural and functional unit of life but virus are not made of cell, they dont use cells in any of their processes.A virus is nothing more than a protein coat surrounding a piece of DNA or RNA,since they are not related to cell theory.
viruses from a exception to cell theory because
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Viruses act an living organism in an host cell but they act as non living in the host cell therefore there is a confusion regarding weather to place virus in living or non living hence it is an exception to cell theory