Final answer:
In laboratory cell culture, contact inhibition refers to the phenomenon where normal cells cease dividing upon contact with other cells. When cell density increases, the cells touch, signaling them to halt division. Cancer cells, lacking this regulation, continue to proliferate without exhibiting contact inhibition, forming stacked layers.
Step-by-step explanation:
When cells are grown in a laboratory, the factor that can stop normal cells from dividing is contact with other cells. This phenomenon is known as contact inhibition. It occurs when cells in a culture become too dense and begin touching each other, which sends a signal to the cells to stop dividing further. In contrast, cancer cells, which are often grown in continuous cell lines in the laboratory, lack this regulatory mechanism and do not exhibit contact inhibition, hence they continue to pile up over one another.