Which of the following cells is drastically depleted by small amounts of radiation (50-70 rem)?

• A. neurons
• B. mature spermatozoa
• C. spermatogonia
• D. muscle cells

Answer: (C)

The main idea here is radiosensitivity: cells that divide rapidly and are less differentiated are much more vulnerable to ionizing radiation than mature, specialized cells. Spermatogonia are the germinal stem cells in the testes that continually divide to produce sperm, so they fit the highly radiosensitive profile. A relatively small dose like 50-70 rem can dramatically reduce their numbers, causing significant depletion. In contrast, neurons and mature muscle cells are highly differentiated and divide little, making them comparatively resistant to such low-dose radiation. Mature spermatozoa are also mature and non-dividing, so they’re not depleted as drastically as the germinal spermatogonia.