How does mitotic activity affect cell radiosensitivity?

• A. Frequently dividing cells are more sensitive to radiation.
• B. Quiescent cells are more sensitive.
• C. Radiosensitivity is unaffected by cell division.
• D. Specialised cells always more sensitive.

Answer: (A)

Radiosensitivity increases with how actively a cell divides. When cells are frequently in the cell cycle, especially as they approach division, their DNA is more exposed to radiation damage and repair before division is underway is limited. Ionizing radiation often causes double-strand breaks, and if a cell is about to mitose, it has less opportunity to fix these breaks, making the damage more likely to be lethal. This is why tissues with high cell turnover—such as bone marrow, the lining of the gut, and germinal tissues—are notably more radiosensitive. In contrast, quiescent or highly differentiated cells divide less and typically have more opportunities for accurate repair, so they tend to be more radioresistant. Thus, the idea that frequently dividing cells are more sensitive best reflects the observed relationship between mitotic activity and radiosensitivity.