Which term describes rod-shaped bacteria?

• A. Coccus
• B. Spirillum
• C. Vibrio
• D. Bacillus

Answer: (D)

Rod-shaped bacteria are described as bacilli. In microbiology, shapes are used to categorize bacteria, with cocci meaning spherical, bacilli meaning rod-shaped, and spirilla or spirochetes referring to spiral forms. The term bacillus can refer generally to a rod-shaped bacterium, and it also names a genus that includes many such species. The other shapes described by the options correspond to spherical (cocci), spiral (spirilla), and curved/comma-shaped rods (vibrio), none of which match the rod form. So the correct term for rod-shaped bacteria is bacillus.