What are the common shapes of bacteria?

• A. Cocci, bacilli, and spirilla
• B. Mites, fleas, and ticks
• C. Rods, spheres, and spirals
• D. Viruses

Answer: (A)

Bacteria are commonly described by their shapes: cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped). This three-shape framework comes from what they look like under a microscope and helps with identification and communication about what you’re dealing with. Cocci appear as little spheres, bacilli as tiny rods, and spirilla as curved or spiral forms, which covers the most familiar bacterial forms you’ll encounter.

The other options don’t fit because mites, fleas, and ticks are arthropods, not bacteria, and viruses are not bacteria either. The phrasing with rods, spheres, and spirals points to the same shapes but uses nonstandard terms; standard microbiology uses cocci, bacilli, and spirilla, which is why this choice is the best match on most exams.