Select false statement about bacterial flagella:

Question

Accepted Answer

The correct option is 2: Made up of tubulin protein.

This statement is the *false* one regarding bacterial flagella, which is why it is the correct answer to the question. Bacterial flagella are not composed of the protein tubulin; instead, their primary structural component is a globular protein called **flagellin**. Tubulin is the hallmark protein of *eukaryotic* motility structures, such as eukaryotic cilia and flagella, where it forms the core 9+2 arrangement of microtubules. In contrast, the bacterial flagellum is a much simpler, helical filament that rotates like a propeller, a mechanism and composition fundamentally different from the complex wave-like beating motion of eukaryotic flagella. Therefore, stating that bacterial flagella are made of tubulin confuses the molecular biology of prokaryotic and eukaryotic cells, a key distinction in cell biology.

The incorrect option is 1: Not surrounded by plasma membrane.

This is a **true** statement about bacterial flagella and thus an incorrect choice for the "false statement" question. Unlike the flagella of eukaryotes (like sperm or protists), which are extensions of the cell membrane, bacterial flagella are completely extracellular structures. They are essentially protein appendages that are synthesized and assembled outside the cell cytoplasm. The structure originates with the basal body embedded in the cell wall and membrane layers, but the visible, whip-like filament component extends outwards, beyond the cell boundaries, and is not encased by a continuous plasma membrane.

The incorrect option is 3: Show a range in number.

This is also a **true** statement and is thus an incorrect choice. The number and arrangement of flagella are highly diverse among different species of motile bacteria, a feature used for classification. For instance, some bacteria are **monotrichous**, possessing a single flagellum at one end. Others are **amphitrichous** (flagella at both ends), **lophotrichous** (a tuft of flagella at one or both ends), or **peritrichous** (flagella distributed all over the cell surface). This variety demonstrates that the number of flagella is not fixed but shows a wide range, depending on the genus and species of the prokaryote.

The incorrect option is 4: Composed of filament, hook and basal body.

This is a definitively **true** statement describing the highly conserved architecture of the bacterial flagellum, making it an incorrect option. The bacterial flagellum is a sophisticated molecular machine divided into three major structural parts. The **filament** is the long, helical, external portion responsible for propulsion, made of flagellin. The **hook** is a short, curved segment that acts as a universal joint, connecting the filament to the cell envelope. Finally, the **basal body** is the complex, rod-like structure embedded in the cell membranes and cell wall, containing a series of rings that anchor the entire apparatus and serve as the motor that drives the rotation.