What are the thin filamentous extensions that the motile bacterial cells have from their cell wall called?

Correct Answer: Flagella

Motile bacterial cells possess thin, filamentous extensions from their cell wall called flagella (singular: flagellum), which enable them to move through liquid environments.

Detailed Explanation:

1. Flagella: Bacterial flagella are long, thin, thread-like helical appendages that extend from the cell wall and cell membrane. A typical bacterial flagellum consists of three main structural components: the filament (the long outer region), the hook (which connects the filament to the motor), and the basal body (which anchors the structure into the cell wall and plasma membrane and acts as a rotary motor).

2. Pili: Pili are elongated tubular surface structures made of a specific protein called pilin. They are mainly involved in conjugation (transfer of genetic material between bacterial cells) rather than motility.

3. Fimbriae: Fimbriae are small, bristle-like fibers sprouting out of the bacterial cell surface. They function primarily in attachment to surfaces or host tissues, not in active locomotion.

4. Lamellae: Lamellae are internal membranous structures or folds found in photosynthetic bacteria (like cyanobacteria) that contain photosynthetic pigments, and are not extracellular extensions for motility.

Therefore, the thin filamentous extensions that motile bacterial cells have from their cell wall are called Flagella.