Biology · Cell: The Unit of Life · NEET
No. The 9 means 9 peripheral DOUBLETS (each doublet is a pair of joined microtubules) arranged in a ring. The 2 means 2 SINGLE central microtubules. So the peripheral 9 are doublets, but the central 2 are singlets. Do not add them into one number — NEET tests whether you know the peripheral ones are doubles and the central ones are singles.
In the AXONEME (the shaft of the cilium/flagellum) the 9 peripheral units are DOUBLETS. Triplets belong to the CENTRIOLE and basal body, which have a 9+0 pattern of 9 peripheral TRIPLETS and NO central tubules. So: axoneme = 9 doublets + 2 central (9+2); centriole/basal body = 9 triplets + 0 central (9+0). This swap is a very common trap.
The axoneme is the microtubule core that runs along the length of a cilium or flagellum, parallel to its long axis. NCERT says the core is called the axoneme and it "possesses a number of microtubules running parallel to the long axis." The whole axoneme is covered by the plasma membrane. In NEET 2024 matching, Axoneme was matched to Cilia and flagella.
Both are outgrowths of the cell membrane with the same 9+2 axoneme. The differences are size and job: cilia are SMALL, work like oars, and are usually MANY per cell — they move the cell or move the surrounding fluid. Flagella are LONGER, usually FEWER, and are mainly responsible for the movement (swimming) of the cell itself.
Both a cilium and a flagellum emerge from a centriole-like structure called the BASAL BODY. The centriole/centrosome forms this basal body. Remember: centriole makes the basal body, and the basal body anchors the axoneme.
The 2 central tubules are joined by BRIDGES and wrapped in a CENTRAL SHEATH. Each peripheral doublet is joined to the central sheath by a RADIAL SPOKE — there are 9 radial spokes in total (one per doublet). The peripheral doublets are also joined to each other by LINKERS. Knowing these connectors (bridge, central sheath, radial spoke, linker) helps in match-the-column questions.
No. NCERT clearly states the prokaryotic (bacterial) flagella are STRUCTURALLY DIFFERENT from eukaryotic flagella. Bacterial flagellum has three parts — filament, hook and basal body — and does NOT have the 9+2 microtubule axoneme. Only the eukaryotic cilium/flagellum has the 9+2 axoneme.
Match List I with List II: List I: A. Axoneme B. Cartwheel pattern C. Crista D. Satellite List II: I. Centriole II. Cilia and flagella III. Chromosome IV. Mitochondria Choose the correct answer from the options given below:
Microtubules are the constituents of:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Both. Cilia and flagella share the exact same 9+2 axoneme structure. They differ only in length and number, not in the internal microtubule pattern.
Nine. Each of the 9 peripheral doublets is connected to the central sheath by one radial spoke, so there are 9 radial spokes.
No. The two central microtubules are SINGLE tubules (singlets), connected by bridges and enclosed in a central sheath. Only the 9 peripheral units are doublets.
The basal body is a centriole-like structure with a 9+0 arrangement of 9 peripheral triplets of tubulin and no central tubule. The centriole forms the basal body from which the cilium or flagellum grows.
No. Bacterial (prokaryotic) flagella are structurally different, made of filament, hook and basal body, and lack the 9+2 microtubule axoneme. The 9+2 pattern is only in eukaryotes.
