Which term describes a rod-shaped bacterium?

Which term describes a rod-shaped bacterium?

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

Answer: (A)

Bacterial shapes are described with specific terms, and the one for a rod-shaped form is bacillus. Think of the rod-like cells as straight, elongated cylinders, which is why we use bacillus (singular) and bacilli (plural) to describe that morphology. It’s common to see the genus name Bacillus (capitalized) used in taxonomy, but when we’re talking about shape, the term remains bacillus. In contrast, coccus describes spherical bacteria, spirillum refers to a rigid, spiral-shaped organism, and vibrio describes a curved, comma-shaped bacterium.

Bacterial shapes are described with specific terms, and the one for a rod-shaped form is bacillus. Think of the rod-like cells as straight, elongated cylinders, which is why we use bacillus (singular) and bacilli (plural) to describe that morphology. It’s common to see the genus name Bacillus (capitalized) used in taxonomy, but when we’re talking about shape, the term remains bacillus.

In contrast, coccus describes spherical bacteria, spirillum refers to a rigid, spiral-shaped organism, and vibrio describes a curved, comma-shaped bacterium.