Final answer:
Plaques are clear areas on an agar plate that indicate where viral lysis of host cells has occurred, as opposed to bacterial growth which forms colonies.
Step-by-step explanation:
The areas of disintegrated cells caused by viral multiplication in cells on an agar plate are known as plaques. These clear areas on a bacterial lawn result from the viral lysis of host cells. When viruses infect cells in a monolayer on an agar plate, they proliferate and cause the cells to lyse. This cell destruction grows outward as the virus spreads to neighboring cells, creating a visible clearing, or plaque, which is a direct indication of viral activity.
In contrast, when individual bacteria grow and reproduce on an agar plate, they form visible masses called colonies. Each colony represents the progeny of a single bacterial cell, and all members of a colony are typically genetic clones of the original cell.
The term that refers to multinucleated cells formed when many host cells fuse together during viral infections is syncytia, not to be confused with plaques which represent areas of cell lysis.