Cilia and Flagella
சீலியா மற்றும் பிளாஜெல்லா
Do not confuse cilia with microvilli. Cilia are motile outgrowths powered by microtubules; microvilli are non-motile extensions of the plasma membrane for absorption. NEET examiners love this distinction to test your fundamental clarity.
The idea
Cilia and flagella are hair-like outgrowths of the cell membrane. The core, called the axoneme, possesses a 9+2 microtubule arrangement. Nine doublets of radially arranged peripheral microtubules surround a pair of centrally located microtubules. This structure emerges from the basal body, a derivative of the centriole.
Why it matters
They provide the mechanism for locomotion in unicellular organisms and the movement of fluids over the surface of cells in multicellular organisms.
NEET lens
Focus on the 9+2 arrangement and the basal body origin. NEET frequently asks about the difference between prokaryotic and eukaryotic flagella; remember, prokaryotic flagella lack this 9+2 microtubule structure. Memorize the axoneme cross-section diagram from NCERT; it is a high-yield visual question.
Clinical significance
Immotile Cilia Syndrome, or Kartagener syndrome, occurs due to defective dynein arms in the axoneme. This leads to chronic respiratory infections and infertility, as sperm motility is compromised. Structure dictates function; when the 9+2 arrangement fails, the body fails.
Introduction
Cilia and flagella are hair-like projections from the cell surface, made of microtubules in a 9+2 arrangement, used for locomotion and moving substances.
Core concept
Structure: 9 peripheral doublet microtubules + 2 central single microtubules (9+2 arrangement) in axoneme. Basal body at base (9+0 arrangement, similar to centriole). Movement powered by dynein protein (ATPase — uses ATP). Cilia = short, numerous, beat in coordinated waves. Flagella = long, few, whip-like.
Go deeper
Dynein arms connect adjacent outer doublets. ATP hydrolysis causes sliding of doublets relative to each other → bending motion. Primary cilia (9+0, no central pair) are immotile, used for sensory functions (in kidney, inner ear cells).
From Class 10
Some cells have tiny hair-like projections that help in movement or moving substances. These are cilia and flagella.