Biology · Cell: The Unit of Life · NEET
No. This is the most tested trap in NEET. Only the flagellum causes motility (movement) in bacteria. Pili and fimbriae are surface structures too, but NCERT clearly says they do NOT play a role in motility. Their job is attachment only.
A bacterial flagellum has three parts: (1) filament, (2) hook, and (3) basal body. The filament is the longest part and it sticks out from the cell surface to the outside. The hook connects the filament to the basal body, and the basal body anchors the flagellum in the cell.
Pili are elongated (long) tubular structures made of a special protein. Fimbriae are small, bristle-like fibres that sprout out of the cell surface. Fimbriae are known to help attach the bacteria to rocks in streams and also to host tissues. Both are for attachment, not movement.
No. Bacterial (prokaryotic) flagellum is a simple thread made of the protein flagellin, with three parts (filament, hook, basal body). Eukaryotic flagella have a 9+2 microtubule pattern (axoneme) covered by plasma membrane. They only share the name; the structure is very different. NEET sometimes uses this to trap you.
No. Bacterial cells may be motile or non-motile. Only the motile ones have flagella. Bacteria also show a range in the number and arrangement of flagella (one, few, or many, at different positions on the cell).
The bacterial flagellum is made of a protein. The filament, its longest part, is built of the protein flagellin. Remember this is different from eukaryotic flagella, which are made of tubulin microtubules.
Select the wrong statement
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Only the flagellum gives motility (movement) to bacteria. Pili and fimbriae do not help in movement.
Fimbriae are small bristle-like fibres that help attach the bacteria to rocks in streams and to host tissues. This attachment can help bacteria cause infection.
From outside to inside: filament (longest, sticks out), then hook, then basal body (anchors the flagellum in the cell).
The filament of the bacterial flagellum is made of the protein flagellin. This is different from eukaryotic flagella, which are made of tubulin.
NCERT Class XI describes pili only as elongated tubular structures made of a special protein. Their role in bacterial conjugation (transferring DNA) is covered in higher classes; for NEET Class XI purposes, pili and fimbriae are surface attachment structures and are not motility structures.
