Final answer:
In a laboratory bacterial cell culture, plaques refer to clear areas where a virus has infected and lysed host bacterial cells, leading to visible clearings in the bacterial lawn. Each plaque represents the progeny of a single virus infecting surrounding cells in a circular pattern. The quantity of plaques correlates with the viral titer.
Step-by-step explanation:
In a laboratory bacterial cell culture that has been infected by a virus, plaques are areas in which the virus has spread and left behind the remains of dead cells. When viruses, such as bacteriophages, infect bacterial cells, they can cause lysis (disintegration) of the host cells. The clearings on the bacterial lawn, visible in the petri dishes, indicate where the host bacterial cells have been lysed by the virus, creating plaques.
Each plaque represents a clone of a single virus, which has infected a bacterial cell and then released progeny viruses that infect surrounding cells, resulting in a circular area of cell destruction. This is a common method used for viral titration, as the number of plaques correlates with the viral titer. Scientist can culture viruses in vitro using cell culture flasks or petri dishes containing a dense layer of bacteria and observing the formation of these plaques among the cloudy bacterial lawn.