What are the three common shapes of bacteria?

• A. Coccus, Rod, Spirillum
• B. Bacillus, Coccus, Filament
• C. Amoeba, Coccus, Spiral
• D. Virus, Rod, Capsule

Answer: (A)

Bacteria are commonly categorized by their shape, which leads to three familiar forms: cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped). This trio is the standard way scientists summarize bacterial morphology, so listing cocci, rod-shaped, and spirillum covers the main basic shapes you’ll encounter. The other options mix organisms or features that aren’t used to describe bacterial shapes: amoeba is a different kind of single-celled organism, viruses are not bacteria, and terms like capsule or filament refer to structures or growth forms, not the basic single-cell shapes. So focusing on cocci, rod-shaped, and spirillum best represents the three common bacterial morphologies.