Q.68 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.

Correct Answer: (D) Flagella originates from basal body.​

Bacterial flagella serve as key motility structures in many prokaryotes, essential for CSIR NET Life Sciences preparation. Option D accurately describes their anchorage and assembly from the basal body embedded in the cell membrane.​

Option Analysis

Length Range (A)
Bacterial flagella typically measure 5-20 μm in length, far exceeding the 0.5-2 μm stated, though minimal motility requires about 2-3 μm. This makes A incorrect for standard descriptions.​

Fibrils Composition (B)
Flagella consist of a single helical filament from flagellin protein subunits forming a hollow tube, not multiple adjacent fibrils with regular patterns—that describes eukaryotic flagella (9+2 arrangement). B is incorrect.​

Conjugation Role (C)
Primary function involves locomotion via rotation; recent studies show flagella aid conjugation indirectly in specific cases (e.g., Bacillus subtilis mechanosensing), but not as a direct “helper” universally. C is incorrect.​

Basal Body Origin (D)
Flagella assemble from the basal body, a rotary motor with rings (MS, LP, C) anchoring the rod, hook, and filament, transmitting torque for propulsion. This is correct.​

Bacterial flagella basal body origin drives motility in prokaryotes, a core topic for CSIR NET aspirants studying microbial structures. These helical appendages, powered by proton motive force, enable swimming toward nutrients or away from toxins.​

Structure Components

• Filament: Longest part (5-20 μm, 20 nm diameter), flagellin polymer in helical tube for propulsion.​

• Hook: Short (55 nm) flexible joint linking filament to rod.​

• Basal Body: Membrane-embedded rotary motor with rings (C, MS, P, L) and rod; flagella originates here via type III secretion-like export.​

• Overall: Hollow axial structure rotates up to 1000 Hz.​

Functions and Arrangements

Flagella primarily confer motility, with arrangements like monotrichous (single polar) or peritrichous (all over). They bundle for run-tumble chemotaxis but rarely aid conjugation directly.​

Key CSIR NET takeaway: Basal body anchors and powers bacterial flagella, distinguishing from eukaryotic versions.​