Final answer:
To pluralize a medical term ending in 'um', replace '-um' with '-a', such as 'bacterium' to 'bacteria' or 'ovum' to 'ova'.
Step-by-step explanation:
To pluralize a medical term that ends in um, you should replace the -um with -a. For example, the plural form of bacterium is bacteria, and the plural form of ovum is ova. This rule is a standard convention in the pluralization of Latin-derived medical terms.