Question

Which one of the statements about bacterial flagella is correct?

• A. Flagella varies in length ranging from 0.5 to 2 μm.
• B. Flagella are adjacent fibrils with regular patterns.
• C. Flagella helps in conjugation.
• D. Flagella originates from basal body.

Hint:

Flagella are for motility, pili are for conjugation. Always recall the three parts of bacterial flagella: filament, hook, basal body.

Answer 1

The Correct Option is D

Step 1: Structure of bacterial flagella
Bacterial flagella are long helical filaments made of the protein flagellin. They function in motility (swimming, swarming, chemotaxis). A flagellum has three main parts:
Filament – long, whip-like helical structure.
Hook – curved connector between filament and basal body.
Basal body – rotary motor embedded in the cell envelope (cell wall + membrane).
Step 2: Origin of flagellum
The basal body is the organizing centre and anchoring point. The flagellum originates from the basal body and rotates like a motor to propel the bacterium. Step 3: Elimination of wrong options
(A) Incorrect – Bacterial flagella are much longer (10–20 μm or more), not limited to 0.5–2 μm.
(B) Incorrect – They are not adjacent fibrils; they are single protein filaments.
(C) Incorrect – Conjugation is mediated by pili (sex pili), not flagella.
(D) Correct – Flagella originate from the basal body.