Final answer:
Biological tissue shows the least radiosensitivity when radiation exposure is prolonged over time, allowing for better repair, particularly in tissues with rapidly dividing cells.
Step-by-step explanation:
Biological tissue is least radiosensitive under conditions where radiation exposure is spread out over a longer period, rather than received in a short, intense burst. Rapidly dividing cells, such as those in bone marrow, intestinal tissues, hair follicles, and reproductive organs, are the most sensitive to radiation. However, in the context of prolonged, low-level radiation, tissues can repair more effectively, reducing radiosensitivity. Studies on mice, which are biochemically similar to humans, suggest that the human body may also be more resilient to low doses of radiation over extended times, indicating that not all radiation exposure is equally damaging, unlike the linear relationship seen in fruit flies.
Regarding types of radiation, alpha particles are the least penetrating but can be the most damaging if they reach sensitive tissues. Alpha radiation from radioactive sources typically has a range of less than a millimeter in biological tissues, which is usually not enough to penetrate even the dead layers of skin.