Which statement best describes how growth phase affects irradiation susceptibility?

• A. Logarithmic phase reduces susceptibility compared to stationary.
• B. Stationary phase makes organisms more susceptible than logarithmic.
• C. Logarithmic phase makes some organisms more susceptible at low doses than stationary.
• D. Growth phase has no effect on irradiation susceptibility.

Answer: (C)

Growth phase affects how cells respond to irradiation because their metabolic state and DNA handling change as they transition from rapid division to a resting state. In logarithmic (exponential) growth, cells are actively duplicating DNA and dividing, which creates many DNA targets for radiation. Damage that blocks replication or breaks DNA strands can be more lethal when a cell is in the middle of replication, and the rapid use of resources for growth can transiently limit the immediate deployment of repair processes. This makes some organisms more susceptible to low doses of irradiation during log phase than during stationary phase, where metabolic activity is reduced and stress-response and repair systems are more readily engaged. It’s important to remember this isn’t universal for every organism or dose level, but the pattern described captures how growth state can increase sensitivity at low irradiation doses in many cases.