Which of the following pairs have a 9+2 arrangement?
  1. Centrosome and centriole
  2. Cilia and flagella
  3. Centrosome and flagella
  4. Cilia and centriole


The correct option is B Cilia and flagella
There are a few structures in the cell which are made up of cytoskeletal elements, such as centrosome and centriole. Centrosomes are found in animal cells only and are made up of 2 units called centrioles. Centrioles lie perpendicularly to each other. They are surrounded by an amorphous pericentriolar protein and form a cartwheel type of arrangement. Each centriole is made up of 9 peripheral fibrils (tubules). Each fibril is made up of 3 (triplet) microtubules. Fibrils are made  up of tubulin. The central region is called the hub which is connected to the tubules by spokes. There are no tubules in the centre. This gives rise to a 9+0 arrangement (9 peripheral and 0 central).

The locomotory structures found in eukaryotic cells are cilia and flagella. Cilia are short hair like processes with oar like movements. They are shorter and more numerous. 
Eukaryotic flagella are the extensions of which arise from the basal body. They are very different from prokaryotic flagella. They are longer and whiplike and made up of tubulin proteins. They are less numerous. Structurally, eukaryotic cilia and flagella are almost similar. The cilia and flagella extend from the plasma membrane. It is hence entirely covered by the plasma membrane. Basal bodies are cylindrical structures which contain 9 triplet microtubules. 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 (9) microtubules, and a pair of centrally (2) located microtubules. This gives rise to the 9+2 arrangement.

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