Which of the following contains single flagella?
**Core Concept**
Flagella are whip-like structures composed of microtubules that provide motility to certain microorganisms, such as bacteria and some eukaryotic cells. The presence and number of flagella can vary greatly among different species, influencing their ability to move and interact with their environment.
**Why the Correct Answer is Right**
Flagellated bacteria, such as *Bacillus subtilis*, typically possess a single flagellum that enables them to swim through their surroundings. The flagellum is composed of a basal body, a hook, and a filament, which are arranged in a specific structure to facilitate movement. The flagellum is powered by the rotation of the basal body, which is driven by the action of the motor protein, FlrA.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because, although some bacteria possess a single polar flagellum, others may have multiple flagella or no flagella at all.
* **Option B:** This option is incorrect because, while some bacteria have a single flagellum, others may have a single polar flagellum or multiple flagella.
* **Option C:** This option is incorrect because, although some bacteria have a single polar flagellum, others may have multiple flagella or no flagella at all.
**Clinical Pearl / High-Yield Fact**
It's essential to note that flagellated bacteria often exhibit a characteristic "end-over-end" motility pattern, which can be observed under a microscope. This pattern is distinct from the "tumbling" or "swarming" motility patterns exhibited by other bacteria.
**Correct Answer: C. Bacillus subtilis. Bacillus subtilis**