Question

Which of the following is not a physical method for controlling microorganisms?

• A. Radiation
• B. Filtration
• C. Disinfection
• D. Desiccation

Hint:

• Physical methods of microbial control use physical means:
  • Heat (autoclaving, dry heat)
  • Radiation (UV, gamma rays)
  • Filtration
  • Desiccation (drying)
  • Low temperature (refrigeration)
• Chemical methods use chemical agents (e.g., alcohols, chlorine).
• Disinfection is a \textit{process} aimed at reducing pathogens, which can be achieved using either physical or chemical methods. It is not a physical method per se.

Answer 1

The Correct Option is C

Methods for controlling microorganisms can be broadly categorized into physical methods and chemical methods. Physical methods use physical means to kill or remove microorganisms. Examples include: % Solution Solution: Methods for controlling microorganisms can be broadly categorized into physical methods and chemical methods. Physical methods use physical means to kill or remove microorganisms. Examples include:

• Heat: Moist heat (autoclaving, boiling, pasteurization) and dry heat (hot air oven, incineration).
• Radiation (option a): Ionizing radiation (X-rays, gamma rays) and non-ionizing radiation (UV light).
• Filtration (option b): Physically removing microbes from liquids or air by passing them through a filter with pores small enough to retain the microbes.
• Low Temperatures: Refrigeration and freezing (inhibits growth, may not kill all).
• Desiccation (Drying) (option d): Removing water, which inhibits microbial growth as water is essential for metabolism.
• Osmotic Pressure: Using high concentrations of salt or sugar to create a hypertonic environment, causing water to leave microbial cells.

Chemical methods involve the use of chemical agents (disinfectants, antiseptics, sterilants, antibiotics) to kill or inhibit microbial growth. Disinfection (option c) is a process or outcome, not a specific physical method itself. Disinfection refers to the elimination of most or all pathogenic microorganisms (excluding bacterial spores) on inanimate objects. Disinfection can be achieved by either physical methods (e.g., UV radiation, boiling) or chemical methods (e.g., using alcohol, chlorine, aldehydes). Since disinfection is a general term for a process that can be achieved by various means (both physical and chemical), and the other options (radiation, filtration, desiccation) are specific physical methods, "Disinfection" is the one that is not a physical method itself, but rather a goal. \[ \boxed{\text{Disinfection}} \]