Medical Terminology Practice Test 2026 – Comprehensive Exam Prep

The idea here is how Latin‑derived nouns change when they become plural. Bacterium is a singular term for a single microbe, and many words ending in -um form their plural by changing the ending to -a. So bacterium becomes bacteria in plural usage. This is the standard, widely accepted form in biology, and you’d say “a bacterium” for one and “bacteria” for more than one. Alternatives like bacteriums or bacterae aren’t used in modern scientific writing, though you might see older texts vary.