Final answer:
The most common physical agent used to control microbes is heat, which kills microbes by altering their membranes and denaturing proteins. Methods like autoclaving are highly effective for sterilization, while boiling is less reliable due to endospore survival.
Step-by-step explanation:
The most common physical agent used to control microbes is heat. This method is effective because it can kill microbes by altering their membranes and denaturing proteins. The thermal death point (TDP) refers to the lowest temperature at which all microbes are killed in a 10-minute exposure, while the thermal death time (TDT) indicates the length of time necessary to kill all microorganisms at a specific temperature. Heating techniques like cooking and canning are classic examples.
However, not all forms of heat treatment are equally effective against all microbes; for instance, boiling does not reliably sterilize materials due to the survival capabilities of some endospores. Sterilization methods that use high heat, such as autoclaving, are more dependable for ensuring the elimination of all forms of microbial life, including endospores.
Other physical agents for microbial control include radiation, filtration, and refrigeration, but heat remains the most commonly applied method due to its broad effectiveness and accessibility.