A virus is just nucleic acid inside a protein capsid. A bacteriophage has a head (capsid + DNA), a tail and tail fibres to grip a bacterium. ▶ Play to highlight each part and its job.
A virus can only multiply inside a host. In the lytic cycle it attaches, injects its nucleic acid, makes the cell build new viruses, they assemble, and the cell bursts (lysis). ▶ Play to step through it.