Which factor significantly affects the radiosensitivity of a cell?

The stage of the cell cycle significantly affects the radiosensitivity of a cell because cells are not uniform in their sensitivity to radiation at different phases of the cell cycle. For instance, cells are generally more sensitive to radiation during the M phase (mitosis) and late G2 phase, as these phases involve active division and critical cellular processes that are vulnerable to damage from radiation. Conversely, cells in the late S phase are typically less sensitive because they are engaged in DNA synthesis, and thus have mechanisms in place to repair damage more effectively. The varying degree of sensitivity during these phases highlights the importance of the cell cycle in determining how radiation affects cellular integrity and function.

While factors such as cell size, tissue type, and age of the individual can influence radiosensitivity, they do not directly relate to the inherent biological processes occurring during the cell cycle phases, making the stage of the cell cycle a more critical factor in this context.