Question

'Cart wheel' structure is shown by

• A. flagella of bacteria
• B. Centrioles
• C. flagella of eukaryotes
• D. both 1 and 2

Answer 1

Answer: (B)

Centrioles

Answer 2

The 'cart wheel' structure is a characteristic feature of centrioles.

1. Flagella of bacteria: Bacterial flagella are simple structures made of flagellin protein and lack the complex microtubular arrangement seen in eukaryotic flagella or centrioles. They do not exhibit a 'cart wheel' structure.

2. Centrioles: Centrioles are cylindrical organelles found in most eukaryotic cells. They are composed of nine evenly spaced peripheral triplets of microtubules. These peripheral triplets are connected to a central proteinaceous hub by radial spokes, giving them a distinct 'cart wheel' appearance. This is referred to as a 9+0 triplet arrangement.

3. Flagella of eukaryotes: Eukaryotic flagella (and cilia) have a characteristic internal structure called the axoneme, which typically consists of nine peripheral doublet microtubules surrounding two central single microtubules (a 9+2 arrangement). While the basal body from which eukaryotic flagella arise has a structure similar to a centriole (9+0 triplet arrangement with a cartwheel), the flagellar shaft itself does not have the 'cart wheel' structure. The question specifically asks about the 'cart wheel' structure, which is the defining feature of centrioles.

4. Both 1 and 2: Since flagella of bacteria do not show the 'cart wheel' structure, this option is incorrect.

Therefore, the 'cart wheel' structure is shown by Centrioles.