Bacterial Flagellum — Filament, Hook, Basal Body Three-Part Architecture
📚 Practice ConceptBacterial cells may be motile or non-motile. If motile, they have thin filamentous extensions from their cell wall called flagella. Bacteria show a range in the number and arrangement of flagella. Bacterial flagellum is composed of three parts – filament, hook and basal body. The filament is the longest portion and extends from the cell surface to the outside.
Bacterial flagella have a 9+2 microtubule arrangement similar to eukaryotic flagella.
BACTERIAL flagella have a filament-hook-basal body structure (no microtubules). EUKARYOTIC flagella/cilia have the 9+2 microtubule axoneme.
Bacterial flagellum = 3-part (filament-hook-basal body), rotates. Eukaryotic flagella/cilia = 9+2 microtubules, beats. Pili = attachment, not movement.
- Bacterial flagellum has 3 parts: FILAMENT (longest, external), HOOK (curved connector), BASAL BODY (anchor in cell wall/membrane).
- Eukaryotic flagella and cilia: 9+2 microtubule axoneme arrangement; ATP-driven beating motion.
- Pili are TUBULAR PROTEIN structures used for attachment / conjugation (not for movement).
- Cilia = short hair-like beating structures (also 9+2); flagella = longer (in eukaryotes). In bacteria, flagella are structurally unrelated.
Match the structures with their descriptions: Column I: A. Pili B. Bacterial flagella C. Eukaryotic flagella D. Cilia Column II: i. Tubular protein structures for attachment ii. 9+2 microtubule arrangement iii. Filament-hook-basal body system iv. Short hair-like beating structures
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Correct answer: D — A-i, B-iii, C-ii, D-iv
A-i: Pili are tubular protein structures used for ATTACHMENT (and conjugation). B-iii: Bacterial flagella have the FILAMENT + HOOK + BASAL BODY architecture — NCERT exact. C-ii: Eukaryotic flagella have the 9+2 microtubule axoneme arrangement. D-iv: Cilia are short hair-like beating structures (also 9+2 internally, but the external appearance is short hair-like). The classic NEET trap is swapping ii and iii — assuming bacterial flagella have the 9+2 microtubule system. They do NOT — that arrangement is exclusively eukaryotic.
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