Final answer:
Heat and time are the two variables that contribute to thermal death time, which is used to describe the time needed to sterilize a sample by killing all its microbes at a certain temperature.
Step-by-step explanation:
The two variables that contribute to thermal death time are heat and time. Thermal death time is the amount of time required to kill all microbes within a sample at a given temperature. It is a concept used primarily in microbiology to ensure the sterility of microbiological media, especially during processes like autoclaving where both temperature and exposure time are crucial for effective sterilization.
Temperature plays a major role in determining how quickly microorganisms will be inactivated, as high temperatures are required to denature proteins and destroy cellular structures within microbes. Furthermore, the exposure time necessary to achieve sterility depends on the temperature applied; higher temperatures can reduce the time needed, while lower temperatures require longer exposure times for the same sterilizing effect.