Final answer:
Enveloped viruses are the most susceptible to high temperatures because their lipid bilayer envelope can be disrupted by heat, leading to inactivation.
Step-by-step explanation:
The organism most susceptible to high temperatures among the options given is E) enveloped viruses. Enveloped viruses have a lipid bilayer derived from the host cell membrane, which is sensitive to environmental conditions like temperature. High temperatures can disrupt this lipid bilayer, leading to the inactivation of the virus. In contrast, other options such as bacterial endospores and cysts of protozoa are known for their extreme resistance to environmental stresses, including high temperatures. Fungi and mycobacteria are generally more resistant than enveloped viruses but not as much as endospores or cysts.
Among the options given, bacterial endospores are the most susceptible to high temperatures. Bacterial endospores are thick-walled structures that can withstand extreme conditions, such as high temperatures, desiccation, and chemical disinfection. Their tough outer layer provides protection, but it also limits their metabolic activity. Once the temperature rises above a certain threshold, the endospores can be destroyed through heat treatments like autoclaving.