In short
A virus is a tiny infectious particle made of genetic material in a protein coat. It can multiply only inside the living cell of a host.
A virus is much smaller than a bacterium, about to . It has either DNA or RNA, never both. It has no cell membrane or cytoplasm, and it does not respire or grow by itself. It takes over the host cell and makes it produce more viruses. Viruses cause influenza, measles, polio and COVID-19. Antibiotics do not work on viruses, but vaccines can prevent many of them.
A bacteriophage is a virus that infects bacteria. It injects its DNA into the bacterial cell, and after a short time the cell bursts, releasing dozens of new phages.
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