9+2 Microtubule Array in Cilia — NEET Biology
✅ Asked in NEET 2024The electron microscopic study of a cilium or the flagellum show that they are covered with plasma membrane. Their core called the axoneme, possesses a number of microtubules running parallel to the long axis. The axoneme usually has nine doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules. Such an arrangement of axonemal microtubules is referred to as the 9+2 array. The central tubules are connected by bridges and is also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublets by a radial spoke. Thus, there are nine radial spokes. The peripheral doublets are also interconnected by linkers. Both the cilium and flagellum emerge from centriole-like structure called the basal bodies.
NTA tests the structural organization of the axoneme, specifically the 9+2 arrangement of microtubules in cilia and flagella. Students commonly confuse the arrangement or forget that there are 9 peripheral doublets PLUS 2 central tubules. The key mistake is memorizing wrong numbers like 9+1 or 8+2. Remember: 9 doublets arranged radially around the periphery, 2 single microtubules at the center, connected by radial spokes and linkers—this is the hallmark of motile cilia and flagella. This ultra-structural detail is fundamental because it explains how these organelles function and appears frequently in MCQs about cell organelles and their organization.
Match List I with List II. List-I A. Cilia B. Endoplasmic Reticulum C. Mitochondria D. Kinetochore List-II I. Spindle fibres II. Cristae III. Axoneme IV. Ribosomes
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