Which statement describes stem cells in the context of radiosensitivity?

• A. Undifferentiated (stem cells)
• B. Fully differentiated cells
• C. Mature neurons
• D. Red blood cells

Answer: (A)

Radiosensitivity is highest in cells that are undifferentiated and actively dividing. Stem cells fit this profile because they are not specialized and retain the ability to proliferate to replenish tissues. When radiation damages DNA during these divisions, stem cells are prone to cell death or loss of regenerative capacity, so they are the most sensitive cell population in many tissues. That's why tissues rich in stem or progenitor cells—like bone marrow and intestinal lining—show early radiation effects. In contrast, fully differentiated cells are usually not actively dividing and are more resistant to radiation. Mature neurons are post-mitotic and hardly divide, so they’re relatively radioresistant. Red blood cells are enucleated and non-dividing, contributing to their lower radiosensitivity compared with stem cells. Therefore, describing stem cells as undifferentiated best captures their high radiosensitivity.