Which organism requires the highest dose of radiation to kill, and what is that dose (approximately)?

• A. Viruses — about 10–200 kGy.
• B. Bacteria — about 1–5 kGy.
• C. Fungi — about 0.5–2 kGy.
• D. Prions — about 100–300 kGy.

Answer: (A)

The question is about how much ionizing radiation is needed to inactivate different kinds of infectious agents. The key idea is that different organisms have different resistance to radiation, so the dose required to achieve sterility varies. Looking at the ranges given, viruses are associated with needing a relatively high exposure—up to about 200 kGy for many virus types—to ensure inactivation. This makes viruses the most demanding group among the options in terms of the radiation dose required. Bacteria and fungi, in comparison, are associated with much lower ranges (roughly 1–5 kGy for bacteria and about 0.5–2 kGy for fungi) in this context, so the viruses stand out as needing the higher dose. The takeaway is that, when comparing these categories under these stated values, viruses require the highest irradiation dose to achieve inactivation.