Mosby Protection-Safety Practice Test

Oxygen availability is the key factor that increases radiosensitivity. When cells are well oxygenated, the free radicals produced by ionizing radiation react with DNA and become fixed in a form that the cell cannot easily repair. This fixation of damage makes it much harder for the cell to survive and reproduce, so radiosensitivity is higher. In contrast, when there is little or no oxygen (deoxygenated tissue), those radicals can be repaired or dissolved before they cause permanent damage, so the cells appear more resistant to radiation. Among the scenarios listed, being fully oxygenated leads to the greatest sensitivity because the oxygen effect directly enhances the damaging impact of the radiation. The other options don’t increase radiosensitivity in the same reliable way: deoxygenated tissue is more radioresistant, and factors like being near the skin or slowly dividing do not guarantee higher sensitivity—the presence of oxygen is the dominant influence here.