Which sterilization method is less effective than steam and requires higher temperatures and longer exposure?

• A. Dry heat sterilization
• B. Steam sterilization
• C. Filtration
• D. Ionizing radiation

Answer: (A)

Moist heat transfers energy to microbes much more efficiently than dry heat. Dry heat sterilization uses hot, dry air, so heat moves by conduction slowly and more resistant organisms, including spores, require higher temperatures and much longer exposure to achieve sterility. That’s why dry heat needs around 160–170°C for extended periods (often 1–3 hours), whereas steam sterilization uses moist heat that penetrates and denatures proteins quickly at about 121°C for minutes. Filtration and ionizing radiation sterilize by other mechanisms, not by heating, so they don’t fit the scenario of a heating method that’s less effective than steam and demands higher temperatures and longer times.