Which statement best describes the relationship between mitotic activity and radiosensitivity?

• A. Radiosensitivity increases with higher mitotic activity
• B. Radiosensitivity decreases with higher mitotic activity
• C. Radiosensitivity is unaffected by mitotic activity
• D. Radiosensitivity depends on tissue location

Answer: (A)

The main idea here is that radiosensitivity increases as cells are more actively dividing. This relation is rooted in how ionizing radiation damages DNA and how cells respond during the cell cycle. Cells that are proliferating are less differentiated and have a greater tendency to undergo division, which means DNA damage has a higher chance of becoming lethal because the cell cannot properly repair and complete division. In the cell cycle, mitotic cells are particularly vulnerable, with many being most sensitive during mitosis itself or in late G2, while cells in S phase—where DNA synthesis and repair are active—tend to be more resistant.

Because tissues with high mitotic turnover, like bone marrow or intestinal lining, show greater sensitivity to radiation, and tissues with low mitotic activity, like muscle, are more resistant, the statement that radiosensitivity increases with higher mitotic activity best describes the relationship.