Biology · Cell: The Unit of Life · NEET
The centriole is 9+0. It has nine peripheral fibrils but NO central tubules, so the centre is empty (that is the '0'). The 9+2 pattern belongs to the axoneme of cilia and flagella, which has nine peripheral doublets PLUS two central microtubules. Quick rule: centriole = 9+0 (triplets), cilia/flagella = 9+2 (doublets).
A cartwheel is an old wooden wheel with a central hub and spokes going out to the rim. In a centriole, the central hub is a proteinaceous part in the proximal (base) region, the rim is made of the nine peripheral triplet fibrils, and radial spokes made of protein connect the hub to the triplets. This spoke-and-hub picture is why NCERT says each centriole has 'an organisation like the cartwheel'.
TRIPLETS. Each of the nine peripheral fibrils of a centriole is a triplet (three microtubules joined). The adjacent triplets are also linked to each other. This is a common trap: cilia and flagella have doublets in the 9+2 axoneme, but the centriole (and basal body) has triplets.
No. The centrosome is a NON-membrane bound organelle. The centrioles inside it are made of tubulin protein and are surrounded by amorphous pericentriolar material, but there is no lipid membrane around them. This matters for NEET, because centriole/centrosome, ribosome and nucleolus are the classic non-membrane bound structures.
No, almost all plant cells lack centrioles and a centrosome. Centrioles are found in animal cells. This is one standard difference between plant and animal cells: animal cells have centrioles, plant cells do not (yet plant cells still form a spindle during division by other means).
They have the same 9+0 triplet structure. A centriole is the structure that lies inside the centrosome and helps form spindle fibres. When a centriole moves to the base of a cilium or flagellum and anchors it, the same structure is then called a basal body. So NCERT says 'the centrioles form the basal body of cilia or flagella'.
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:
Match list I with list II. List I: A. Nucleolus B. Centriole C. Leucoplasts D. Golgi apparatus List II: I. Site of formation of glycolipid II. Organisation like the cartwheel III. Site for active ribosomal RNA synthesis IV. For storing nutrients Choose the correct answer:
Microtubules are the constituents of:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
9+0 means nine peripheral fibrils around the edge and zero (none) in the centre. The nine peripheral fibrils are triplets of tubulin, and the middle has only a proteinaceous hub with radial spokes, not microtubules.
The centriole forms the spindle fibres that make up the spindle apparatus during cell division, so the centrosome helps in cell division. Centrioles also form the basal body of cilia and flagella.
Centrioles are made of tubulin protein. Each has nine evenly spaced peripheral fibrils, and each fibril is a triplet. The central hub and radial spokes are also proteinaceous.
No. The centrosome and its centrioles are non-membrane bound. They are surrounded only by amorphous pericentriolar material, not a lipid membrane.
The hub is the proteinaceous central part in the proximal region of the centriole. It connects to the peripheral triplets through radial spokes, giving the cartwheel look.
