Which cell type is severely depleted by small amounts of radiation (50-70 rem)?

The correct answer is that spermatogonia are severely depleted by small amounts of radiation, specifically in the range of 50-70 rem. Spermatogonia are germ cells located in the testes that undergo meiosis to produce sperm. These cells are particularly sensitive to radiation exposure because they are actively dividing.

Radiation can cause damage to the DNA within these rapidly dividing cells, leading to cell death or mutations. In contrast, neurons, mature spermatozoa, and muscle cells are more differentiated and have a lower rate of division, making them less susceptible to radiation damage at the levels mentioned. Neurons and muscle cells are post-mitotic, meaning they do not divide after reaching maturity, while mature spermatozoa are also not in an active state of division. Therefore, spermatogonia, given their high level of proliferation, are highly affected by radiation, resulting in depletion when exposed to relatively low doses.