A spherical bacterium is called a:

A. boiling water: Boiling water is a physical method of microbial control that kills most vegetative cells and some viruses through denaturation of proteins and disruption of membranes. It does not involve chemical agents, making it a physical means of sterilization or disinfection.

B. pasteurization: Pasteurization is a controlled heating process used to reduce microbial load in liquids such as milk and juice. It uses heat as a physical agent to destroy pathogenic microbes while preserving the quality of the product.

C. HEPA filters: High-efficiency particulate air (HEPA) filters physically remove microorganisms from air by trapping particles. This is a mechanical, physical approach to controlling microbial contamination in healthcare and laboratory environments.

D. ultraviolet radiation: UV radiation damages microbial DNA and prevents replication. It is a physical method of disinfection commonly used on surfaces, air, and water.

E. hydrogen peroxide: Hydrogen peroxide is a chemical disinfectant and antiseptic. It kills microbes through oxidation and production of reactive oxygen species. Since it is chemical rather than physical, it does not belong in the category of physical agents for controlling microbial growth.

A microorganism that is not motile and has stopped metabolizing is not necessarily dead. Some microorganisms can enter a dormant or quiescent state under adverse conditions, such as nutrient deprivation, extreme temperatures, or exposure to antimicrobial agents. In this state, metabolic activity and motility may temporarily cease, but the organism remains viable and capable of resuming growth and reproduction when favorable conditions return. True microbial death is defined as the irreversible loss of the ability to reproduce under optimal conditions, regardless of temporary changes in metabolism or motility. Therefore, absence of movement or metabolic activity alone does not confirm death.